how can I find floor plans for an extra room on the back side of my house?

14X16. Door to outside on end of room, double french doors for entrance, two slider windows or one large window on each side.

I did something similar. I hired a draftsman/architect to create the necessary plans for the building contractor. I don't remember how much it cost off hand. However, it was a simple project and he was an independent as opposed to an employee of a larger company so he gave me a pretty darned good deal.