depends on the size, then determine how many curves and cuts your going to have to make (takes alot of time). Then figure out how long it'll take you to remove the old stuff, grade, and install the new stuff. Most of my installs are about 1200-2500sq feet. We can remove a 1200sq ft lawn in about 90minutes, grade it in 30, and it takes us about 20min per pallet to lay with 2 guys and 700sqft per pallet. Then ya cut, and depending on the curves, it might take 10min, it might take an hour.
Then figure out all your costs with the data you gathered and give them the quote....
Or just go the short easy way and charge per sq foot, but If its hilly and theres alot of cuts I dont do that, I only really charge per sq foot if its one big rectangle.
I have 2 lawn installs saturday, one at a customers front lawn, and then my front lawn Sense im already going to have the sod cutter rented, why not do my own lawn ya know. LOL.
However at the customers house I dont think I will be laying the sod until next week due to a sprinkler system has to get installed, but the tearout is still on sat.