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http://www.fishandtips.com/ I used this website's plans to build my tank stand. Its cool because you put the dimensions of your tank in and it will give you a customized plan for building your stand. I used 4x4's to build the stand for my 125g which I think was overkill but i deffinitely didn't want to take any chances. If you have any more questions let me know. Like i said i just did this project myself!
do a google for 'DIY aquarium canopy' and you'll get a lot of resources.
i'm not too handy, so I just build a 3 or 4 sided box, then attach a top piece, hinges, and then the flip open lid section. then just put some blocks inside so it can rest on the edge properly, and you're good.
definitely used a topcoat sealer, or an oil based paint on the interior to prevent moisture from getting in and warping the boards.