I just built one out of a 30g for my 90g display. Not sure if mine is the best but I read up a bunch. It is pretty simple. Get the largest tank you can fit in your stand and you can divide it into 2-3 chambers. You need 2 minium. The intake chamber which the water from your tank empties to. You also put your Skimmer in this chamber if you have one since the skimmer works best with "dirty" water directly from the tank. The other chamber is the return. This houses the return pump. I also have my heater in there. I have a third chamber which is a refuguim. You can also just fill that chamber with live rock rubble for extra live rock if you don't plan to run a refuguim. I have the return as my second chamber and the refuguim as the third. The refuguim is being fed by a maxi-jet 600 from the intake chamber and overflows into the return chamber. I did this because i wanted to control my flow in the refuguim but this is a matter of taste. A lot of people make the refuguim the second chamber. You will need a bubble trap baffle between the intake/skimmer chamber and the second chamber since you don't want to feed bubbles back into the display. This is very easy to create. I had two pieces of glass cut to the width of the tank and 1/2 the height. The third is the width of the tank and 1'' shorter than the height. Attach one of the smaller pieces where you are dividing the chamber at the bottom of the tank. Then take the large piece and attach it so it goes to the top of the tank leaving 1'' open on the bottome. You attach this 1/2'' from the first then attach the the other smaller piece 1/2'' from the large piece attached to the bottom. You want the water to go over the first under the second and over the third.
There are pictures on my build out thread in this forum