Welcome to the forum! I would recommend starting with some tried-and-true design parameters which you can then modify to suit your specific needs:

[link]http://www.uoguelph.ca/~antoon/hobby/pmdesign.htm[/link]

Additionally, I would recommend looking at Turbocad (free program) for making and preserving your drawings. There are many building methods and materials to choose from. You can learn a great deal by reading the stickies in the building forums. Good luck with your future projects!