Attach batten to sheet metal

[Masajäkel]

I am going to build an outdoor staircase and need to attach one side's beams to a framed sheet metal wall. What type of screw should be used to ensure the beams are securely attached? Expander, molly, or do you have other suggestions?

 

[Masajäkel]

Was there no one who could give advice?

 

[snoooze]

If you can screw into the studs behind the metal sheet, that is probably preferable.

What type of metal sheet is it?

 

[Masajäkel]

It would have been great, but the reglar behind are not where I want to mount the reglar for my stairs. So there will be a cavity behind, which means I can only attach to the metal sheet.
Common corrugated metal sheet