I recommend the following. Put an EZ Kleen bait station (Item #1061), baited with Contrac Bait Blox (item#1180) every 40 feet around the perimeter of the entire building. You might not have to do it right by the front door, but the more the better, especially if there are vacant fields, dumpsters or other inviting areas in close proximity to your facility. The holes and flat side need to be put up against the wall. You can also secure these stations to patio blocks so they don't walk off if you want to.
On the inside, I recommend putting an Aegis RP (Currently not listed on website) rodent station with a Snap E Rat Snap Trap (bigsnapE), every 20 to 30 feet along the interior walls. I would bait these snap traps with dates or black licorice pieces. Same thing as above…put the side with the holes flush up against the wall. Place stations everywhere, but especially in areas of high activity (visible droppings or gnaw marks). These traps have to be checked every 5 days if not sooner. However, rats are neophobic, and anything new in their environment causes them to be very cautions. They might have to get used to both the external and interior traps. Be patient.
Rats run walls. All traps have to be placed with the holes closest to the walls where the rats can run through them. They will hit the traps or bait on the outside.
As for the ceiling, my concern is not killing rats…that is easy… it is keeping them from dying in those sensitive areas that will smell if you cannot get to them. You can't just put rat traps up there and expect it to catch a rat. You might have to put up with occasional smells till the problem is gone…which might never happen. Typically this is an ongoing maintenance issue.
As long as there is no food material being stored and distributed I have no problem recommending putting rat baits into the false ceiling.
There is a brand new pest control product on the market called FirstStrike Soft Bait Rodenticide that comes in soft packs. I recommend them they are great for high pressure areas. Put 3-4 packets every 10 ft around perimeter of building up in the ceiling and attic areas. There is a chance of a dead rodent, however this will put a big impact on the problem.
There are 364 of these bait packets per pail and the cost is $74.99 per pail. One pail will do the entire facility, when concentrating on the ceiling areas.