Online booking system- reports

Hi,
I would like to be able to run a capacity & efficiency report on online bookings. Ideally in the Booking Counts report there would be an additional column showing spaces available.

But, if that's not possible then a report showing how many spaces are available during a time period which could be filtered by category and offering. Also filter by cancelled and active courses. I could then compare this with the Booking Counts by event date to show how many spaces were actually taken.

Thanks!
Audrey