I've made many fake room mic tracks. Many different ways to achieve it. No rules, here are a few steps to quickly mimic a mono room mic. This can also work in stereo. I like to do this before i've processed the raw drums so it mimics a mono raw room mic. No rules though.
1. Make sure all drums panned mono sound good with little phase problems. Good practice anyways.
2. Balance the levels of the drums, keep some headroom here. Generally keep the cymbals quite low here or out entirely. I have a tendency to want a bit more snare and toms in my room mic and a bit less kick. Totally your choice and no rules here.
3. Print the new mono track, and apply a decent reverb on it. Usually most will have a decent starting point preset. I use waves rverb and it has a drumroom preset. Anything can work. The goal here is to make the fake room mic track sound "roomy/distant"
4. Room mics have a delay due to the distance between the source (drumkit) and the mic. Feel free to push this track behind a very little bit to give it the effect of distance. WATCH FOR PHASE ISSUES. Just like if you were placing the room mic in the room.
You now have a "mono room mic"
6. No rules here but generally a low pass filter rolling off some highs and crushing the hell out of it with compression works for me.
Hope this is helpful.
