There are a few things that you need to consider very carefully. Firstly how big is the college? Unless it is sizeable, you will probably never get enough customers in to cover your overheads. You can get a good idea by checking out the colleges own cafe/restaurant to see how much custom they pull in (although this is not a sure fire way of telling if a competing business will be succesful or not).
The college will probably either charge you a rent or a portion of the profits. If your turnover is going to be lowish, it may be better to go for the portion of profits rather than a set rent regardless of your turnover.
Or they could go for a combination of both. As they have approached you to open up in the college, you are in quite a strong position, I would try to negotiate a rent free period and try to get a stepped rent/portion charge increasing, say over the first 3 years,
Although it is great that the college have approached you, I would ask myself why? If things were that good, why do they want to share profits with another business instead of keeping all the custom for themselves? I would ask them that question directly.
Another thing to consider is to try to get a no competition clause into the lease, that will stop any other competing business opening up in the college and taking all your hard won customers away. I can tell you that as an owner of a national franchisee sandwhich chain, if I saw that a competing business was doing well and I had the chance to open up and take their trade, I would go for it!
Best of luck, I hope if you decide to go ahead, it goes well for you, but do as much research as you possibly can before going ahead.
Sue