Backdrop help

Your looking for help on how to paint something like the scenery in the pictures? If that's the case, I wouldn't be much help as I've only gotten as far as painting mine a very bright blue color. Still, there should be somebody on here that can give you some pointers as I've seen quite a few threads showing how theirs was done.
 


I too painted a blue sky, and an engine gray shade below it, but want to paint a backdrop along one wall. I also want to paint behind pine trees in spots so it will look like there are more without spending tooo many $$$$$$$$$$$$ in actual scale trees.​