First off get yourself some graph paper and do some decent to-scale drawings with a ruler and a fine tip pencil. I'll use 1 square = 1 foot so I can get into fine detail.
I do all my own drawings for floor plans then bring them to an engineer to CAD and engineer/certify the plan. As someone who has done numerous houses for myself and other people I can promise you that there will be something you'll wish you had done differently with the plan, but for the love of God, don't hire a builder because he is the cheapest!!!