Consultants rather than full time employees?

An experienced carpenter or landscape designer can get pretty expensive to employ full time, especially when you don't always have enough work for them to do. I can always find cheap labor to complete a job, but the expertise is the expensive part, so I thought about attempting to hire a few consultants instead. I may go for retirees with a wealth of experience who are looking for something to do to keep a little busy, maybe a few hours a week. I would give a small base salary whether they worked or not, simply to keep the commitment, then an appropriate hourly rate for the actual time they do work for me. Do you think this is a good idea?