SQL database Queries for booking system

I am building a booking engine for a gym. The gym has multiple locations with opening hours and closures. Each gym will have one or multiple rooms which can hold one or multiple classes which have different operating hours and available slots.

I need assistance with not only a database model (one exists but needs extending) as well as writing some stored procedures to get the available sessions and bookings for users.

UPDATE:

I have added my current database schema (this is a smaller version of the full database, but covers the major tables required for the queries.

I will need to run through the database, and how i am currently storing different values in the database as well as the "nuances" that relate around the project. I have the requirement that I will be adding the concept of Studios and Classes to each location. Currently the database assumes one type of session for one gym (this is not a typical gym business). We will want to provide the ability that there are potentially multiple Studios in a Gym and multiple classes for each studio. Each of these classes will require different operating times for them to be running and also run for variable lengths.