The contract is just for the design work to start. Because I'm design only, I make darn sure I've accounted for everything in my proposal. I've done enough projects at this point that I can get them in the ballpark for what the job will cost (the screen porch $30-40k, patio $20-25k, plantings $10k, etc) so we at least know if what they want designed is realistic for their budget. My design fees run anywhere from $400-500 to $3000-4000, depending on what we're designing.
When I worked for a design-build, we mostly did a flat rate design fee. Everything was $700 for the design, unless there were a lot of grading or framing issues, in which case it was $1200.