How do you build a roof on The Sims 2?

First go to the roof building section. Then you can either select a pre-built roof, or you can build your own. Building is sort of hard especially when the roof turns itself the wrong way. You can choose any of the roof designs, then you drag the roof to whatever way you want. But, if you build a half roof, then make sure you do the other half. And dormers are good for covering up the mistakes you can make. (like if have a 2 foot gap between the sections. XDDD). When you click a design, the little window thing will pop up. It tells which style and way the roof can go. Good luck!