have not actually put it together yet but i taped it together real quick and snapped a few pictures. Hopefully it will give you an idea of what it will look like. It is going to be a hanging canopy but could probably easily be adapted to sit on the tank.
Pretty simple design. Just going to put it together with wood glue when i build it.
I slotted the side boards and then gave the cross members where the lights will be mounted a tab that slides in the side boards.
The canopy is actually sitting upside down right now. Once it is flipped over i will hang it from the pieces sitting against the floor right now. The cross members will not be glued in place. I will leave them to slide so that i can move my lights or if i ever change my lights i can just slide the boards to where i need them in order to mount it all.
The boards in the corners against the floor are just to hold it all together and keep it square. Probably just going to screw in 4 eye holes to hang it from. If there is to much light shining out of the top of the canopy i am just going to get a piece of black fabric to staple to the top. This will still allow the heat to escape and block the light.
Hope that gives you some ideas to start with.