I assume fixing the roof isn't an option.
If you do the pan ceiling, make certain the drain doesn't clog. If the pan collects dust/mold etc - which clogs the drain, you could end up collecting then dumping a larger quantity of water on your equipment than you would have if you did nothing. (And you could still end up with humidity problems, and if the server room DOES have air conditioning, you could end up with problems from condensation.)
Do you have room to build an environmentally controlled room within your space to house equipment? Ideally with a sloped (and waterproof) roof? (Call it physical security, and include temperature AND humidity control.)
Most of the switch closets I've seen don't have their own HVAC. You might get away with putting a sloped pan with a drain over those...
