First of all install the Plugin Manager plugin.

1) I’m having difficulty building the roof,

After you installed the Plugin Manager it's easy to install the Roof Generator plugin. You can read more about it in this thread. Try the last few pages of that thread.

2) creating the stairs for a home with a basement, and

Install the Generate Staircase plugin. This allows you to specify exactly how you want your staircase.

(Click "Recent threads" in the menu bar. The threads for both the roof and staircase are both on the first page.)

3) getting the basement level to appear when viewing the project in 3D.

Right click in the 3D view and select "Display selected level". Select tab with the basement level and you should see your basement.