Autogyro.com has http://www.autogyro.com/technic/specs.htm page. It contains most important parameters for designing an autogyro.

Ten degrees of aftertilt seems be a good starting point. I have eight degrees of aftertilt on [link=http://www.kemi.fi/kk019065/models/gyro2/index.html]my autogyro[/link]. I think the rotorhead design with two plywood triangles with plastic hinge in the middle is very simple and well working.

It might take you some time to design an autogyro. I was successfull on my second attempt to design it. Your project seems interesting. Good luck with it.