Odoo is the world's easiest all-in-one management software. It includes hundreds of business apps:
CRM | e-Commerce | Accounting | Inventory | PoS | Project management | MRP | etc.
Did you try make a CRM case + automated action (Which will create the calendar)? It is a little complicated, but it can give you lights without program.
Sorry but I don't have the time now to make a big example, but read teh book looking for these two concepts, Segmentation on CRM and Automated actions.
You have to create a modul.
Create a model for rooms property, and a simple view to show this model for the users.
Let's start here: https://doc.odoo.com/v6.1/developer/03_modules_1.html/