I need some advice on building a tank lid for pretty cheap.

I have a 40g long terrarium i think?

its 36"x18"x13"

and it has a dual locking lid and a plastic rim. i thought of de-rimming it and building a wood rim

its to temp. house my red tail until i can build a nice enclosure for him and my balls.

he is about 4 1/2' and in a 20 long and he hardly has room to move