I typically price by the hour, so I tend to walk around each individual unit, and figure out how many hours the job would take me + materials, or my employees + materials, then add it up. I a large volume like that, I would take my hourly rate, (for example: $75/hr and reduce it to $65 or 60/hr) and figure it out with the volume prices. Definatly leave yourself some wiggle room, for the unforseen circumstances.
I got burned bad on a job because it was 45 minutes away everyday, I was paying two guys to ride with me up to it, and we had to go everyday for two months. When I bid the job, I was not aware that they were getting ready to begin renovation on the only highway heading up to the job. Therefore, everyday my 45 minute drive turned into 1- 1.25 hr drive both ways. You can do the math, and figure out that after two months that takes a pretty large hit on the price of the job.
So be careful, big jobs are great, but also somewhat risky.