We often do quotes based hand drawings done on graph paper. This is fine for doing quotes. However, we highly recommend having an architect or designer draft up some plans for your project. Building with no plans is like driving across the country without a map or GPS. You will likely get there, but it will take longer and cost you more in the end. Having a good set of plans is like a road map for your project. It will take the guess work out of the project for your contractor. The end result is a home with no surprises for the home owner.
We have a couple designer/architects that we can recommend if you need one for your project. The cost for plans is usually a minor percentage of the total project costs.