Question from a client

1

I was working on a website and cd cover for a client and after we had a meeting I showed them my sketches of some ideas I had for a new logo. I just got an email from them asking if I can make the logo digital and send it to them. Now, I’m not a fool thats going to just do it for free. But how would I tell them politely that I’m not going to just give them my designs for free? Should I use a contract?