I'll give it a try anyway..
You decide if it is too difficult to make.. I think it's peanuts and very straight foreward, nothing much can go wrong.
Simple diagram.
Acrylic sheet 4mm would be sufficient and can be cut with a knife..
The 2 x pieces with the diagonal sides kit them to the inside of the light stands legs.
The 1 x narrow piece is excact same size as the top surface of the light.
Than order a set of these acrylic hinges, i guess preferably 6 for a 90cm lenght. 3 each side.
https://www.banggood.com/45x38mm-Do...-Folding-Hinge-Plexiglass-Hinge-p-979682.html
Now glue the hinges to the narrow acrylic top sheet that rests on top of the light. Than glue the 2 larger flaps again to the hinges.
You can also apply a few kit dots to the light and kit that sheet to it. If you ever want to remove it again, take a piece of nylon fishing line. put it between light and acrylic sheet and cut it off. No damage done.
Anyway, that way you have a complete transparent lit, with 2 flaps that can open.
Obviously make the flap size not to stick over the glass outside the tank. But a few milimeter shorter, than any condensation water will run back into the tank.
I can't think of anything simpler, cheaper and easier and effective to make.