Questions about hood and lights

I am considering getting a 75 gallon aquarium that I would use for
tropical fish with plants. In pricing hoods and lights for such an
aquarium, they are very expensive. Is there any reason why I could
not cover the aquarium with glass and then build a light fixture on
top of that which is basically an oak case for a standard two bulb 48"
flourescent fixture?? As long as I keep it dry, a standard fixture
would work, wouldn't it?

Thanks

Mark