Hi,
I'm wanting to replace a rotted shed door with something that will
better withstand the weather. I'm thinking it'll have a 2"x4" frame
and with either 1/4" or 1/2" plywood. What materials could I use to
have a long lasting, maintenance free door?

I've purchased a Trax (Trex?) 2"x4" for the bottom part of the frame
(too heavy to use for the entire frame).

The door will be painted, so the materials will have to take paint.

TIA
Todd