I'm building a house and using stairs for the look of the roof. Will monsters spawn up there at night (assuming I'm sufficiently far away)? Do I have to put torches up there to prevent that?

2 Answers

You do not need to put torches up there. Passive mobs spawn on grass only (at least in grassy areas...), aggressive mobs spawn on cube-blocks only. No steps, no slabs etc.

Edit. As mentioned in comments, monster can be spawned in upside-down stairs, at least in 1.4.6 version (which is old, though)
Here you may check it for 1.8 version:

7

As of Windows 10 Edition, today a skeleton spawned on the roof of a librarian's house, which is made of wooden stairs only.