I just made a canopy for my 15g based on some pictures from Melev's site. Here is
Melev's design, here is a picture of the one I
built for mine before it was finished. Here is a
full tank shot, you can see pretty well how the canopy turned out in relation to the stand, and here is an
inside shot.
When I built my canopy, I simply went to the local BORG, picked out a nice 2' x 4' piece of 3/4" plywood and had them cut it to the dimensions I needed. I went during the middle of the day so they were not busy by any means and were more than happy to do my exact cuts at no extra cost. I had a large piece that was left from the cuts, I used this as a level base to build the canopy on. A square, wood glue, wet rag and duct tape was all I needed, and it turned out pretty well I think.
Is it just a standard AGA, 16"x8"x10"? I would look to use 1/4" plywood, though you will probably have a hard time finding a nice flat sheet of 1/4", or even 1/2". If ultimately you cannot find a decent sheet of plywood, MDF board could possibly be used, but you would have to seal it quite well. I am building a remote sump cabinet out of 1/2" MDF at the moment, and I plan to do 3 coats of polyurethane inside and out
and then put down some Formica inside as another barrier.
I'm not sure what type of lighting you'll be using, presumably PC on that size tank? Use the dimensions of your lighting to build your canopy and you should have no trouble at all.
Cheers,
Marty