call a contractor. sometimes they have contacts and information that you need without hiring another party.
Run on down to your local building department, they can give you a set of guidelines for doing your own drawings. The inspectors are very helpful in this regard and will tell you what they want to see
Look around for a book with different styles and the plans included. Maybe Home Depot or B&N. Ask around and check your newspaper for people that build garages but make sure and check them out big time. My buddy just got a 24×36 for about $7K.
The outside of another good contractor if he is on top of that.
My upstairs bedroom and added large bilevel deck using plans and plans built dormer on my upstairs bedroom and they were second lowest but also offered free delivery truck to replace few studs that were warped wow.