Asking her out

I met a girl in my apartment building today after the fire alarm went off and we both ended up on the same sidewalk waiting for the FD to clear the building. She initiated conversation and we talked for like 15 minutes about where we are from, our cats, what we do for work, etc. She is super cool. We walked back to our apartments and turns out, she lives like 2 doors down from me. I didn't end up asking for her number or anything but I think I would like to ask her out to this work event that's happening in like a month. Should I just knock on her door at some point and be a brave man or maybe write a note?