I don't know about women, but guys make friends with women they have crushes on, all the time. I see it every day. If you are a gay guy trying to make friends with a straight guy you have a crush on, it will never work out, because, well...you are gay, and he is straight.
Being "friends" with someone first (straight or gay) can work, but only if you don't smother them too much. Keep it light and casual. Also, it would be better to let them know what your intentions are, sooner, rather than later, because if you don't let them know, they are gonna assume you are only interested as a friend, and it's never gonna go anywhere. Not only that, but if you wait months, or even years to tell them what your intentions are, if they aren't interested, you will have wasted all that time pursuing someone that isn't interested.