Asking a guy out at high school

So I'm a sophmore in High School, and I'm going to ask this guy out tomorrow. I know he is gay, and we are friendly with eachother, but we aren't really part of the same friend groups. The thing is, I have no idea how to ask him out. I have 5th period choir with him (whcih is right before a 40 minute lunch break) and I also have 7th period chem and 8th period gym (8th is the last period in the day) with him. When do I ask him out? What do I say? So far, my best plan is to ask him after school "Do you want to get some ice cream in town together after school sometime?" That way, its up to him whether its a date or just friends, but it does sound like a date. Thoughts? Advice?