I would suggest studying the production of a certain breed when creating your own. Studying how it was done and with what dogs will be a good tool for you when choosing how to create your own theoretic breed.
May want to do some genetic research as well. Which dogs have good traits and which dogs have more bad traits such as bad hips, eyes, elbows, structure, ect...
This could prove to be a great paper! Lots and lots to learn....
I will post a few links to help get you going
These links are informative on genetic problems that many breeds face today. It will help you select the best breeds to use for your "created" breed.
www.offa.org
http://www.vmdb.org/cerf.html
http://www.optigen.com/
http://www.vetgen.com/
If you have any questions feel free to pm me. I would love to help you if I can.