While I've never made an aquarium from scratch, I have replaced the bottom of a standard 55 galon aquarium, with no leaks, so have a bit of an idea of what you're up against. If you want to go with a really odd or wild size or shape, you may not be able to move the thing. I'd recommend that whatever you do, you look into the "footprint" of the tank you want and how high you want the sides to be. It then should be relatively easy to determine the pounds per square foot that your floor will have to support. Aside from this, you'll also want to consider the depth of the water in your tank when determining the proper thickness of glass. My 55 gal. has about 18" of water (including gravel) and the sides are 3/8" thick and what I would bet are double strength glass. I did a lot of checking around, and purely because I could get it from a salvage yard cheap, I installed a slate bottom to replace the glass. As far as the entire process, I'd recommend having something to support all of your sides that's very solid, since you have to leave it for at least 24 hours for the sealer to set. One hint here, they sell "aquarium" sealer in tiny tubes, but if you are doing anything that's larger, it'll cost a fortune, and you'll constantly be switching tubes. I did a lot of checking to make sure I wasn't going to kill my fish, and found that the standard caulk sized tube of clear silicone sealer was actually the same stuff. I went so far as to call the number on the tube that I had written down on a trip to the local home improvement center. Also, don't be too anxious to put your fish in or you may kill them as the sealer gives off vinegar (acetic acid) fumes for a while after you use it. And, being an acid, not too good for the fish. I waited a couple of days before adding any water to the tank and then anly partway to see if there were any leaks. There were none, so little by little, I added water. Just in case, I did this in the garage, so that any major leak while I was at work wouldn't be all over the floor! If you have any other questions, I'd be happy to try to answer them. I've had the aquarium going for about 3 or 4 years now with no leaks, so it can be done. My parents had made an aquarium completely from scratch, so they may know things that I don't in this regard. If you make an odd sized tank, you'll have to make a custom stand for it, which I did just to save money from 2X6's and 2X4's that I had and a bit of sanding and stain.