I don't think I've ever seen software specifically for estimating scaffolding- it's a pretty "unscientific" item to estimate unless you're talking about scaffolding the Empire State Building or something- divide the length of the wall needing scaffolding by the length of each frame, divide the height of the wall by the height of each frame, and multiply the two to determine the number of frames you need. What exactly are you having problems with?
Bob, when I used to have scaffolding put up they used pipes not frames and there was often a lot to it. Stair towers, cantilevers, trusses over the garage and/or front porch, up and down the hill, etc.
The guy who priced them figured the rent on the material, and he figured a crew would take a day to load up, drive, and set up one job. Then they'd take a day to strike, load out, and clear a job. These were average to large houses.
I use Brand Scaffolding, a nationwide company that rents scaffolding, sells, designs on complex jobs, and does E & D. It's one of those things that I'd rather not worry myself with. They also deal in shoring. A full service scaffolding contractor will also minimize your exposure to OSHA liability by supplying a complete product.