My idea, His design legal advice?

I came up with the idea of a logo for my website but a person I know design it for me free of charge. Now if I start using it to turn a profit do I owe them anything? Also if I get it trademarked will I have to pay him 1st? IF I do have to pay him what would be a fair amount a flat fee or 5% to 10% on commission. New at this don't know how it works.