Combining CSG's to make a prefab?

[Papa Beans]

Just wondering if its possible. Like in this instance:

 

 

http://gyazo.com/beaf4f77ce9c11bcc84f9c6b5239f215

 

 

[the above is a photo]

Thank you

 

 

EDIT::

For anyone wondering you need to go to the Assets tab, then drag one object onto another. Like this:

http://gyazo.com/9c2ee28ed1f95cced94372daa7f50d7b

 

Then right click on stairs and click save as prefab.

 

Forgot to say it. But what he said.

[Einlander]

Then right click on stairs and click save as prefab.