vector - How can I merge two objects in Illustrator?

In Illustrator how can I merge this roof vector to the background of the square?

roof and square

Answer

As @Bart Arondson has pointed out, what you want to use is a clipping mask.

This is how it works:

You need to group your roof-tiles first. Select all of them with the black selection arrow, and use cmd+G or go to Object -> Group.

Then you make sure your square is on top of the roof-tiles group. Pretend this multicoloured pattern is your roof.

Select both roof and box and go to Object -> Clipping mask -> make:

That should give you this result: