Is it okay to let your 10 year old son sleep on the floor in your bedroom?

It's definitely not "illegal" to let you 10 year old son sleep on the floor of your bedroom. However, 10 years old is a little old for still sleeping with your parents (or at least in there vicinity).

What I would do is talk to him about it and see where that conversation takes you. He could say: "im scared..." or "i just like sleeping with you" or "I dont like it in my room". All of which can be overcome.

The next time he asks about sleeping with you, you can say "No son...its time to sleep in your room" (The direct approach) or: "You know what son, lets lay in your room for a while. Ill go with you". This is a great approach because it allows you to see the issues associated with him sleeping in his own room. When he falls asleep, trail off to your room and hope for a good morning :)