If you have access to a good table-saw building a sump from acrylic is pretty straight forward.  I built mine for about $60.  This would allow you to custom size it to you stand, pumps, and skimmer.  Even simpler though, is to use a glass tank and partition it as KeoDog described...

I went to Regional Plastics and had them cut me some 1/4" plexiglass partitions that I siliconed in. I was going to cut them myself but they only charged $5 to make all the cuts.   The first section almost goes to the top of the tank. This is where my skimmer and heaters are. The next section is made of 2 pieces with the water flow going between them to the refugiim. The refugium is about 6" deep with 1.5" substrate and macros.  The final section has a submersible pump in it for the return. You are welcome to come by and look at it if you want.  Just give me a call at 594-2132 durring the day or 816-9359 evenings.  I live in Sandy.

Size of pump needed is determined by how often you want to turn your water over and how much water your overflow system can handle.  What size is your tank?  You can have a glass tank drilled if you want to use an external pump or make your sump out of acrylic like Flaz suggested. Here are some of the best places I've found for Mag pumps.

http://www.aquatictech.com/pumps.html">http://www.aquatictech.com/pumps.html

http://www.petsolutions.com/cgi-bin/cgicatls?l=42">http://www.petsolutions.com/cgi-bin/cgicatls?l=42

http://www.bigalsonline.com/cgi-bin/search.cgi?inSupplier=Supreme+Mag+Drive&inUID=1051124335.1051124335">http://www.bigalsonline.com/cgi-bin/search.cgi?inSupplier=Supreme+Mag+Drive&inUID=1051124335.1051124335

rfoote,  why change pumps?  Glass or plastic can be drilled.  I just don't see a need to buy a new pump.  Those Iwakis are nice pumps.

The easiest method is to do what keodog suggested.  Buy a glass aquarium that will fit under your sump and still big enough to do what you want.  Get it drilled for return pump(s).  Silicone in glass or plastic baffles.

A better approach, imo, is to go plexiglass.  It can be made to any size you desire.  It's easy to work with and probably cheaper then glass, if diy.  I'd be more than willing to help you in this endeavor.  I've got all the tools needed and I wouldn't mind building someone elses sump before I build mine .

Kind of a guniea pig, I've built skimmers before, just never built a sump.  I don't think it would be that much different though.

The pumps do get hot, usually nothing to worry about.  Now imagine that pump in your sump...you might not need a heater!

Glass sumps with bulkheads won't leak any more/less then acrylic ones.  Usually it's the plumbing that leaks.  Speaking of wifes, no matter how sneaky I am, she always seems to catch me when I have a towel in my hand.

Sump size - actually thinking about it I could really go about 10" longer if I did go with a in sump pump.  I figure this would be a good idea to increase my refugium size.

peiji - I have an in sump skimmer and from what I understand you don't want your skimmer right in your refugium.  Is this correct?  Also, if I end up doing a in sump return pump I don't want it right in my refugium sucking up sand, macroalgae and so on.  I believe you also want to do some baffles after your overflow into the sump to stop bubbling of the water returning into the tank.  Any other ideas anybody?  Check out some of the links given on another post I had about cast vs extruded.  I think it was sarnack that gave some good links to examples of sumps/refugiums.

Ryan, sorry about the pm.  I've just purged my inbox.

Here's some sump designs that I like, ymmv:

I like this one because it essentually separates the skimmer water from the refugium water.  I like this idea.  Second choice would be to skim the water before going to the fuge.  I don't like the idea of skimming the water after the fuge.  Also, if I want a big skimmer, which means more water flow through the sump (more water flow then I'd want through the fuge.  I don't think you want the fuge to look like a river do you?

Here are a couple pictures of a sump with a nice bubble zone design.

I actually like the concepts behind the first one quite well.  Why don't you want to skim after your fuge?  I kind of thought that is what you would want to do?  I'm a little unclear how on the first pic. the refuge overflows to the skimmer portion.  I'm guessing the black valves are the inlet?  I was just thinking in the middle of the plexi to notch out a section for overflow.  This looks cleaner though and probably prevents marco and so on from overflowing.

I've set up a sump/refuge thats pretty simple.  It is a 20 gallon tank. It's size is about 30x12x12.  It is divided into 1/3's by two dividers. The dividers are just a underground filter cut to size. Cheap and already made to width. 

The first section is a deed sand bed and has live rock. I aslo use this section for fragging. It is where the water from the tank enters. I have also placed the intake for my evss skimmer there. 

The middle section is deep sand also. It is where my macroalgae dwells.  I currently have 8 types growing here. There is also 3 mangroves living here.To stop the sand from migrating to the 3rd section here I have a foam piece along the bottom 4 inches of the next divider.

The 3rd section is my return area. I currently run a rio 2500 as my return pump. My skimmer is also is placed in this area. The divider and foam stop 99% of and sand getting into this section. Weekly, I do have to trim algae that has grown past the dividers.

I run the sump/refuge on a reverse daylight schedulehad I had a extra icecap 660 around so I have it lit up by two 36inch VHO's.  This seem to stabilize my morning PH. It was very inexpensive to buy and easy to setup.

The tank I'm using it on is a 46 bow front.  It was hooked up to my 80 gal. prior to current test of just using deep sand (7inches) and 2 over the back  emperor filters.The rio 2500 is overkill for the 46.  I have used a rio 1400 and 1700 with good results.

I have The pc from Home depot(American Lighting).  It works fine for the macroalgae. I use the VHO's now because of a heighth clearance challange with the sump under my tank and being able to use it for frags. 

The reason I wouldn't want the skimmer after the fuge is there would be less of a chance of the "bugs" from the fuge getting caught in the skimmer.  The real appeal (to me) of using a refugium is all the mini/macro life abundant in the fuge that works it's way into the main tank.  Any biofiltration would be secondary.  In my ideal world, my refugium would be elevated above the main tank and gravity back, eliminating the return pump.

I like Kahuna's sump.  The skimmer bypasses the 'fuge and it's simple.

hmm, maybe I go overkill on circulation, but I've got a Rio2100 on my 20 gallon tank that I wish I'd bought a 2500 instead.

My refugia is elevated and I highly recommend that.  Gary Williams has a great tank (second only to John Fletcher  ) that utilizes the elevated refugia.  View some CPR setups and see how they work, if you are really interested.  Also, we will be discussing this during our June meeting (presidency recently planned the next few months, and that list will be provided to the webmaster soon). 

Also, cheap lights like those at Home Depot are fantastic for sumps.  Many people have had great success from them.  You can also get blue bulbs and white bulbs to replace the bulb that comes with them.

Adam

Yes the Lights of America lights are what I typically use.  Fixtures are like $30 or $40 for the larger ones.  They wire straight into a regular 120V, no ballast necessary.  They are actually fixtures to put outside on your house.  Somewhat common lights, many people use them on their tanks.  In fact I ran my 35 gal for 5 years with only these lights. 

Anyway, hope this helps

Adam

I just use flexible tubing.  I seem to move things around alot.   I do plan to change to PVC eventually.  I get home Friday night. I'll take photos Sat. and send them then.  What part of the valley are you in.  You are always welcome to come by and check my system out.

Jon - check out these links for some pretty cool designs.

http://www.melevsreef.com/">http://www.melevsreef.com/

http://www.sparklingfloorservice.com/tank/sump_chris.html">http://www.sparklingfloorservice.com/tank/sump_chris.html

http://www.sparklingfloorservice.com/tank/55sump.html">http://www.sparklingfloorservice.com/tank/55sump.html

http://www.sparklingfloorservice.com/tank/design.html">http://www.sparklingfloorservice.com/tank/design.html

Hey, since you all helped in designing this sump, I'll post a few pictures of the progress here.

Here's the sump just before gluing on the bottom.

Here's the sump full of water, testing for leaks.

No leaks, I'll let it sit for a couple hours then polish the edges.