Calling all acrylic pro's

I have messed around making some small handy items out of acrylic. Some of my projects where a test tube holder, a specimen container and a small closed in cube. (not sure i was board)
lol Anyways early to mid summer i will have my own fish room and i have been throwing around the idea of a 75 gallon tank. Well to keep cost down a little i thought about making a 75 gallon cube or a 40 gallon cube out of acrylic. However i am stumbling on the idea of it not holding the water. The bottom i am ok with but how do you support the top? Do i use a sheet of acrylic and cut open a big hole for the lights and all the plumbing?
Thanks in advance
