Ah yeah nice. I had planned a green roof but with 2 big openings and a relatively long span I don't think it'll take the weight unfortunately.
My doors are from slide and fold as well. The 'instructions' are hopeless - clearly meant for people who have installed these things before. It's definitely a 2 person job!
Drilling steel should be fine with some decent HSS bits.
ETA I ordered slideandfold's expressed doors and the lead time was 6 weeks, not the quoted 10 days.