Hiding a part of an object in the Object Mode How can I hide parts of an object in the Object Mode? I need to model different parts (each part has to be a single object) in a big box surrounding them (external object). My task is to model a room and the things contained in it; therefore I need the positions of the different objects in reference to the room's walls and ceiling...

To clarify: this is the room from outside (a simple box)  

whereas this is the same room from inside 

I want to add some features to the room in the inner part but do not know how to hide just some parts (walls and ceiling) of the first object modeled.

E.g. If I want to add the stairs going from the ground floor to the first floor (visible in the 2nd picture) I need to hide walls and ceiling to be able to use right/left/top view. Though being these modeled as part of a single object, making invisible the whole object would hide also the ground and first floor which I definitely need...
you can  use the mask modifier for this task :


create a vertex group of the vertices that you want to hide 
add a mask modifier  and assign the vertex group
you can click beside the vertex group to switch the effect
the mask will also has effect in the render you have to uncheck 'show in render'