How to make buildings for Unity?

I am making a game and it is the first time I have seriously tried to make a full game and I am having problems. The setting for my game is a school, and I planned to be able to go inside, and out, of the school.

How would I go about making all the rooms, corridors, gardens etc… Would I make all the rooms on one model and add different materials, or would I make every room separately and place them together, or would I do something else. I use Blender and GIMP to make my models and I only use the free version of Unity.

Any help is welcome.
Thanks in advance.

You can do this however you wish. I usually model one scene in Blender, but have each part as a separate mesh (child of main)… That way you can UV / Unwrap one thing at a time, but then you can just drag the whole blender scene into Unity with all materials. Make sure to put the blend file and UV maps all in the same folder, then import that whole folder to unity. That way, all the textures will be applied automatically.