Back when we sold retail (Been 12 years) we would include material, weeding, masking in the sqft price. We had a range of sqft pricing to accommodate complex designs. In the end, the goal was to try to simplify pricing in a way that would average our shop hourly rate. Time is really the "thing" you are selling.
Design and installation were extra, or worked into a flat rate of say 1 shop hour minimum.