Legality of software development

So I am a college student, and at my job I made a php website that would be beneficial to where I work. Recently, they have asked me for it. The thing is, programming is definitely NOT part of my job description, and my friend suggested that I should not just give it to them, possibly sell it to them.
I'm not really up with the legality of all this, was wondering if anyone knew.

>>1
Negotiate amicably.
If you made the website during their time with their resources then its theirs.  If you used your own resources and time, and theres nothing in your contract stating you have to give them the source(IE NDA or information only availiable to employees) then be nice. 

Dont say PAY THE FUCK UP OR ILL SUE.  Remember that they would actually be your customers.  Oh, and make sure you talk to someone who cant actually sign off a payment or you are wasting your time. 

Oh and get ready to prove your softwares worth.