where are you located?  parking and max size of hotel are usually covered in the zoning code.  otherwise you can probably find this info in a few different sources (arch graphic standads, neufert, etc...)

Most convention centers post fairly detailed floor plans online for exhibitors.  Additionally, most cc hotels will advertise their key capacity.  Run through some precedents and generate your own ratios based on observation.

For starters, look at the Chicago McCormick Place, Atlanta World Congress Center, Orange County, and Washington DC Convention Centers. 

There is no one-to-one relationship between convention center size and rooms in an attached hotel. Most convention centers (or convention bureaus) will look at total rooms within proximity of a venue, i.e. area accessible to convention center by foot or transit. From there, you would look at occupied room nights per year to achieve profitability. Once you stray into this territory you are leaving the realm of architecture and entering into market analysis and city planning. Important stuff, but outside of your scope, especially as an intern designer. 

The other question you ask about parking spaces per room is a simple zoning code issue and can be found in your local zoning ordinance.

Thanks everyone for your input, it was very helpful. To answer your question toasteroven, I am located in Fairbanks, which is in central Alaska. This is a proposed addition to the University of Alaska Fairbanks main campus.