|I use Tigra calendars, they are very powerful and give very details instructions on their use. |
Once the form is submitted, you can look at the POST results and format it for your query as necessary.
It would be difficult to provide specific code for the POST page without more details about the database structure surrounding room availability; IE: are rooms presumed available unless booked in a "bookings" table, or is there a table containing dates and times that rooms are available, which then become flagged as booked, when a booking comes in, etc. lots of variables to consider.
I hope Tigra helps with the calendar portion!