Is there any window glazing? If so, you are looking at didassembly first. If not, and all you want to do is repaint, carefully apply commercial stripper to the sides and ends, being very cautious about not getting it on the wood. Clean with damp rags.
When it is dry, sand all wood smooth, and apply three coats of lacquer-based sanding sealer, sanding between each coat. Mask the sides carefully, spray flat black on the roof and floor with a rattle can. Once that is dry, you can refinish the sides by again carefully masking your fine woodwork.
Should end up looking like this:
