Panko has it pretty close to right, IF you have time to dedicate whole days 8-12 hours to each step. Unfortunately, it takes me much longer to get a difficult project out. Modeling is by far the longest step in my creations, but rigging and such is right at what Panko says. Also, the less complex the project, say, you don't have treads and wheels, the rigging is much much easier. Figure a month per large project, and 2-3 weeks for smaller projects, down to a day for a simple prop.