How do you subtly flirt with a guy (who is your roommate)?

I do have a crush on my flatmate. It's been a few months and it's not going away. So I kinda want to see if he might feel the same way but for obvious reasons I want to be careful. I don't want to move and we get along well now and I don't want to ruin that.
But at the same time I want him to get the message. So what are some things I can do that are innocent but so that he will get the message?
How do you subtly flirt with a guy (who is your roommate)?
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