SUMIFS for Date Range

here's the basis of my struggles boiled down:

Facts:
I have 5 buildings, each with 100 rooms.
Groups of people enter come and go from different buildings
Groups range in size from 10-100 people
Each group has a specific Entrance and Exit Date

Needed:
determine is a building is in use based on a 'Start Date' column, 'End Date' column, and a reference date
count the occupancy of the room on a day a building is in use


Attached is what I have so far.

Any step in the right direction would help immensely