I had a 5 story fire escape that was steel that looked horrible, I put two guys with sanders and high gloss black paint on it and a few days later we were done. since it is metal you might be able to sand out the rust and weld back any missing metal.I would have that inspected by a local fire alarm person (they often do fire escapes also), you would be amazed at what does not need to be replaced.Also, talk to the fire marshal to make sure any repairs you are planning are good with him, do that early, he will appreciate it.

Your buying a metal building on a concrete slab in a very tertiary market, and if you lose DG, half of your principal is wiped out.

However, thought I would give some insight on metal roofs!

Have seen them made out of cinder blocks holding down metal framed box, or some cheap ones just out of wood. 

W the depth that metallic paint added, it made the whole house look very high class and it was no more difficult than spraying any other coating on.

It taught me a few troubleshooting tips (I already knew how to clean coils and make sure drain lines were clean).Because of this I saved myself several service calls that would have involved a high priced tech replacing; thermostats, exhaust fans and relays.

It is wrapped in metal wire that I'm guessing is about 1/8" thick, at least.

@Patrick Sears I install used central heating and air conditioning equipment...super cheap...example 2013 system, 3 ton, installed with a mega cage with thick expanded metal sides $2000...look on craigslist or call the slightly shady looking AC companies with the beat up 20 year old vans...they always do side work....

You can do you site work at the same time that you're building your container home off site.I've talked to a number of builders that complain about the amount of welding and metal work involved with shipping container homes.

One needs to remove the old drip edge, pre-drill the Hardie Siding and screw it on to the old boards, then install new metal corners and new drip edge on the roof.