Provides shade from the hot summer sun but allows the winter sun to penetrate for maximum solar gain. This reduces heating cost in the winter and keeps out unwanted heat in the summer. Soffit vents and roof vents vent the attic of humidity and excess heat. Cellulose is the lowest cost insulation. A minimum of R-38 is recommend.
Ceiling insulation is critical because heat rises and takes the path of least resistance.
Low, or non-VOC paints are readily available at little or no extra cost. Latex paints are easy to work with. Doors and face frames are solid wood. OSB is used on the interior. Doors could be simple slab doors out of glued up boards.