WesWorld

Has anyone posted a step by step guide for planebuilder?

Not that I'm aware of. There's a fairly comprehensive set of instructions on the second sheet of the workbook, though. My recommendation is to take an aircraft that you've got fairly good specifications for (max weight, length, wingspan, wing area, engine weight, etc) and put in those parts, then tweak the other portions of the sheet and see how things like range, speed, ceiling, etc react.

The instructions on page two of the workbook are fairly complete. As Hrolf said, go for simming historical designs first and then work onwards from there.