I think you can see that the flap on the front is mounted by two hinges that allow it to swing up and rest on the top of the hood while you are feeding or peering in.
This design also has a hidden layer for the ballasts as you can see from the see through veiw i included on the side of the unit. Of course, this will only work right if the flourescents fixtures arent wider than your tank. Otherwise, A simple system of two shelf hangers on the wall behind your tank, coupled with some mylar (space blanket material) wrapped around the sides to keep the light from escaping would work.
Since you've proven yourself to have the DIY gene imbedded in your DNA, The rest of the work to build the unit in the diagram shouldnt bee too hard for you at all!
Good luck and let us know how it's coming along! B)