Hands down, my favorite live recordings are high quality matrixes, so my own glass ceiling would follow the seqence laid out below...
(You'll need one complete audio recording rig and a separate recorder for getting the SBD patch, or a 4 channel recorder with a long pair of cables that reach back to the SBD.)
1) Make arrangements with the sound engineer in advance and confirm with him/her that he/she will have the time and gear (extra SBD channels and cables or whatever might be needed) to provide a soundboard patch that will be dedicated to recording the performance. Make sure you know what output connections exist on his gear so that you have the right cables to patch into your recording gear.
2) On the night of the recording show up for the soundcheck. The recording engineer will of course get the levels for the PA feed set, but then he needs to spend time getting your special SBD patch levels mixed correctly too. Since it's a separate patch, it will be a separate mix too.
Note: For a glass cieling recording, you don't want to record from the PA mix because that mix is mixed for the room and not the patch, and usually sounds like crap later on. The only way to get a perfect patch is have the mix for the patch done separately so that the levels for the patch are correct.
3) During soundcheck, while your soundguy is getting the patch mix perfectly set, you roam the room to figure out the sweet spot for an ambient recording. Obviously, since we're talking glass ceiling here, you probably want to have a fairly good quality recording setup where the mics and preamp is towards the higher end of the gear spectrum. Hoswever, like others have stated, it's more important to get the mics in the sweet spot than to use the highest dollar gear.
4) Before the crowd comes in, set-up your live recording rig in the sweet spot and do whatever you need to do to protect it from the public, including the ass-hats that are gonna yell into mics that aren't high enough...so tape it down and get the mics up high...suspend the mics from the ceiling...whatever you gotta do to get a clean audience recording from the sweet spot.
5) After you have both recordings, synch them together in post using software such as Audition or Soundforge. If you use two recorders, you might have to stretch or shrink one of the recordings to get them time synched together, but it's easy to do with the software. Usually, my experience is that the split will favor the ambient recording, but mix the two to taste.
(Note that if you're using a 4 channel recorder, you might need to adjust one of the recordings backwards a millisecond or two in order to get the two tracks perfectly synched...but the advantage of using the 4-track is that they'll be time synched together (no time drift as the recording progresses). It depends on how far back from the stage the mics are located...the farther back they are, the more the delay that will exist between the ambient recording and the SBD recording. You can tell there is delay in the record when you listen to all 4 tracks together...if you hear a slight reverb that is delay between the two recordings.)
There ya go!