Well there are no blueprints for it, I just had an idea and I built it. Some pet stores have canopy hoods, and if you see how they sit on the tank you can figure out how to make it work.
Mine is made out of 1/4" plywood, and it sits on the tank with 1x2s attached around the inside. As you can see, mine covers up the black plastic rim of the tank.
Drawbacks, you pretty much have to know what kind of filter youre gonna use because youll have to cut holes in the wood for them. The hang on tank filters would probly be really difficult since they would need such a big hole.
If you are going to have a large hole you may want to use thicker wood.
Also, seal the wood very good on the inside. The inside of the hood will be very humid. If the hood is closed it will get quite warm above the water too. I stained the wood then applied about 5 coats of polyeurethane.
Be very careful with your electrical components, as they will be exposed to constant humidity.
If you are going to have a window like mine, expect it to be covered in condensation quite often if the temp inside the tank is different from the room.
Make sure your tank is at a low enough height that you can reach inside when the hood is on. My hood is connected to my filter now, so taking the hood off will be very complicated. Also, even tho the hood is only 1/4" it is still very heavy and awkward.
The photo below is the only blueprint I had. I drew it in Photoshop and pasted it on my tank to see how it would look.
If I could do it all over, I would probly make the hood taller, so the basking lamp would be farther away from the basking area, but I just put a smaller bulb in and get the same result. My turtles enjoy basking away from the lamp when the hood is closed because the heat the hood traps inside.
One other thing I wish I woulda done with my tank is to install lights under it. I think that would look pretty cool, especially if you had it shining up through some plants or through a hole in a rock or something. Well maybe next time.

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