Well I'm not a carpenter but I have built a couple of stands before. Currently my largest stand holds a 125 gallon tank. I think a main concern is the base, if you use 2x4's lay them down flat and then assemble them in the shape you want, followed by the risers or legs. No matter what size stand I'm building I always put at least one center bracing across the middle a) for support b) for door hardware to mount to.
Here is a very rough sketch how I build mine. I typically just use regular 2x4's for frame and center supports and 4x4's for corners but that's overkill imo
for your size aquariums. Then I wrap the outside with plywood and cover with veneer or panel as necessary followed by any decorative trim you might want. I also like a very thick piece of plywood for the top and cover it with a hard foam rubber so the tank will sit nice and level.