Dave nailed it. If you get pleasure from creating stuff, do it. Read a lot about it. Start figuring out what you like by looking at magazines like Fine Homebuilding. Consider how your house fits among your neighbors. Will your addition make it appear out of place? What materials do you want to use? Are they appropriate to your climate? Don't forget to look at how the sun enters your addition during different times of the year. Don't be afraid to get in over your
head. It is a good way to go if you are a tightwad and your spouse is patient. If you run out of money, you let the project sit for a while. good luck