Its not a prelim bid is it? We often get plans that have just the exterior walls and are asked to give a budgetary price for it. Once the owner sees the numbers are in the ball park he then has the E.E. do the real plans. Then we go back and bid the real project.
If he is just trying to get design work for free, I would walk away. If he is cheap at the start, he will be cheap through the whole project.
