If you're always in a hurry and terrible with commitments, I might suggest you rent a storage space or continue parking your forty thousand dollar cars in the driveway and save your garage space for unused furniture, bicycles, unpacked boxes, garden rakes, and lawn mowers. Because, the biggest enemy in do-it-yourself is not the lack of carpentry skills or ability to follow directions, but lack of planning and failure to schedule the time it takes to get the job done.
Build the framework for all four walls. To account for the fact that the front and back walls are different from each other (due to the doorframe in the front) and the side walls must both be sloped (to prevent rain from collecting on the roof), each of these will have to be tackled somewhat differently. It’s easiest to construct the back first, the front second, and the two sides last, as shown in the numbered image below. See How to Frame a Wall for more information before you read the instructions below.