Update. I got the job. Start next week sometime. Going to use my mini ex, Bobcat, and winch to collapse the building so it's safer to work on. Owner is a friend and a customer so I'm going to help them recycle.
I know I can pull a lot of the building apart and at least get it where it will not fall on anyone. Then the fun part begins with the cutting. I have to have everything cut to 18' lengths for the owner to haul away as scrap. I get some of the scrap and I am responsible for a clean slab at the end. Charcoal and little stuff goes in roll-off containers..
I haven't decided on which method to use for cutting, though. I have a torch setup but have explored a plasma (partially because I want one and partially because it would speed the process up and be safer than a saw).
Also have a heavy duty makita sawz-all. Was told that there are some quality demo blades for cutting the corrugated metal and purlins? Anyone try that?
Keep in mind that a lot of the roofing tin will get shredded and balled up by the mini ex so I am mostly concerned with the purlins. The big round posts will probably be recycled for other projects or if they are too warped, scrapped. The I-beams will most likely be reused somewhere on the property.
So it's mostly purlins, bracing, and corrugated roofing metal to worry about. I will unscrew some panels if they are accessible but not going to spend a lot of time on that aspect.
Not sure I want to spend the money on a plasma cutter but it sure looks fun.

Out of time to order one online, though. All I've found local in the $1500 range is a Hobart 500i. Not sure if it's up to the task? Have a Miller Bobcat 225 8kw generator/welder to power it.
Anyway, thanks for the opinions.