Unity FPS level design

I'm looking for an FPS map based around a city theme. The map should be mid range in size with lots of different places to take cover and flank the enemy. Not all the buildings have to be accessible to the player but I do want 1 medium sized building with about 4-5 floors. It needs to be accessible with a designed interior. I want this building to be an office building with multiple stair cases/ways to get to different floors. There does not need to be an accessible roof. The project should be made in unity 3D core.