The parts book just gives 'self tapping screw' sadly. If you have the last parts book (RTC9022B) and any bolt, nut or screw has a part no, but no specs, look it up in the rear index, and mostly the entry will have the length and thread specs. Just not in this case. I am sure somebody who has had their roof off will chime in....eventually.
Per comedian Stephen Wright (Canadian)-
When I was young we had a sandpit.
It was a Quick Sand Pit.
I was an only child.....eventually.
He also lived in a Oneway, dead end street.