If you look at Lowcels gallery (lowcel has a post in Ltpipers "The Light Has Arrived" thread) he has a pic on the 2nd or 3rd page, of his marked up 29 gallon tank that he used for his sump/refugium AND has pics of it under the tank. I used that as a template for my own 29 gallon sump, which I just now got done glueing some of the glass in. I am going to try to take some pics of the step by step of the process & post them here. Its really not as tough as ppl might think. Several of the folks on here have built there own, & have various tales of what worked for them. You will read around the net that you shouldn't use acrylic inserts for glass tanks, because the acrylic doesnt bond well to glass.... I wouldn't pay that too much mind.... I believe both Phil & Jim have used acrylic & glass together with no failures... Phil has a massive sumpfugium that is something to behold, & I believe that Jim posted that he had built not one, but several using that method.
I personally went with glass, because it was cheaper. However, there were a few pitfalls associated with that decision... The main being that I had the gut cut maybe a 16th or two, too short, so it didnt fit snugly. Had I gone with acrylic, that would not have been an issue, because I could have gotten it cut a little big, then trimmed it as it needed. I am not too worried about it, something Phil suggested long ago came back to me & I was (hopefully) able to correct it. I havent finished yet, so I cant say for sure....
Another benefit to acrylic... it wont explode if a rockslides into it.