Once you have been provided a list of available rooms based on your time requirements, you can click on any of the rooms on the list.
A window will appear with 4 tabs: Room Details, Setup Types, Features, and Availability. If you click on the Setup Types tab, you can see all the layout options for that space with capacity.
You can do a search by room capacity. In the left hand column, there is an option Let Me Search For A Room. You can enter a value for Number of People. You will need to hit Search to populate the rooms with the specified capacity.