Cabin & Old Car
Based on Sketches of the whole environment from different perspectives, draw elevations for the cabin and the car (without deformations) using a vector program (Illustrator in this case). Import the elevations into Maya to rough out 3D models and export into a scene. Cheap render viewport and use the picture as a template for paintover. Using rough brushes, paint out the general look of the environment.
Do not concentrate on details, keep it "impressionistic". Details come later, at the production phase of the pipeline (modeling, texturing and visual effects).