Metal Roof and Liner Installation

I'm getting an insert installed tomorrow (yea!). House has a metal roof. Roof system is plywood decking, felt, purlins from top to bottom (ridge to eave) and then metal panels screwed into purlins. How should the installers walk on this (apart from carefully)? Any tips? The house is new to me and I haven't walked on it yet. It is a 2 story colonial. Per them, it doesn't look like it will be possible to lean a ladder up against the chimney 'cause the slope on the ground. Here is a link to a house pic if so interested:

http://www.velvetfoot.com/coppermine/albums/new_house/main.jpg

Well, all went smoothly. No hook ladders to scratch the metal or anything. No dents that I've seen anyways.

Picture of the install ?

Nice house, glad things went well.