Hey, the only way it will ever get done is just to do it. I agree with some of the others in that you probably are going to want to excavate at the side of the house that you want it on, and make sure that you have a proper concrete pad poured for this structure, and then the skies the limit. You could definitely make it out of wood, but unless you know where to get large sized lumber really cheap it's probably going to be cheaper on a tank of this size to go with concrete. Just take a look at johnptc's tank. For a tank that size and depth I would definitely go concrete. Also you can do your plumbing into the concrete instead of having to cut into it later on. Another thing you may want to consider is lighting for reef, or whatever you plan to put into it. You might find that you are spending as much on lights for this tank as you are the tank itself. You are going to want some major humidity controls in place as well, and also plan for your water changes accordingly. Theres a lot to plan into this, and as with any large aquarium I'd say get your spacing and size limits down first. Get google sketchup, and actually design it to your specifications to see if it will work in the space you are looking at. Do research on materials so that you will know what is sound to use. I would imagine that if you are using alluminum braces you will need to have them custom manufactured, and will want to look around for qoutes on that as well as the acryllic which will be hella thick at 15'. I'd say it would be better to bring that down to at least 10' depth, but you could do a design where the tank goes into the groung in concrete. so you would have 2' on top for your filter, 8' for your viewing area, and 5' below that with concrete walls that will still be easily viewable from above. I'd toy around with skylighting to help with that lighting bill also. Anyway good luck, and hopefully there's something useful in my rambling.
