I have a student that uses as few words as possible when speaking and writing. We wanted him to be more descriptive, but he never seemed to get past the stage where sentences were modeled for him. I finally dug out a kit that my children had liked in younger days called Tote 'n Tiles by Discovery Toys. It has a plastic peg board, square and semi-circular pegs, and patterns to copy to make several different designs, all packaged in a neat little kit. My student was instantly intrigued.
In order to get him to say longer sentences, he had to ask for the pegs he needed for a certain row, including the number, color and shape. Therefore, after a couple of models and some cueing, I got longer sentences containing up to three adjectives:
eg. "I want three, blue, square pegs."
It may be a little contived, but it made sense to him, and me. I still love being able to use my own children's old toys.