Really think about if you can handle seeing him at work every day if you did date and it fell apart. That's the biggest downside of dating a co-worker. But if you are willing to take that risk, instead of outright asking him out, put some feelers out as possible starters to guide him into asking you out. Such as before your days off, ask him, "So, do you have anything fun planned for your days off?"
If he answers with whatever he's doing and asks the same of you, you can say something like, "I've been wanting to try this new restaurant (XYZ), so I might do that."
To me, that plants a seed and might guide him into suggesting doing the things mentioned together.
But if nothing happens, whether he doesn't make the first move, or you do or don't have the nerve, I don't think it's in your best interest to progress in this emotional affair, whether one-sided or not. And that's for many reasons. Firstly, bonding with a crush will prevent you from bonding with a single dating prospect. Secondly, once one or both of you are dating others, an emotional affair at work will negatively affect those new romances. Believe me, a partner will learn to know of that work bonding, and emotional affairs are as damaging as physical affairs.
So this forever friendship you fantasize about isn't in the cards no matter how this plays out. True friendships are totally platonic and crushes aren't healthy in the longterm if the friendship doesn't progress to a romantic partnership.
Lots to consider. Good luck and keep us in the loop.