Oil Canning - 24 or 26 gauge - Snap Standing Seam

We are building a new residence with about 2500 square feet of hip roof. The pitch is 4/12. It is located in Ontario, Canada about 200 km north of Toronto.

We want to have a standing seam roof in black with no striations or ribs.

According to the manufacturer of the product (a Canadian member of the MRA), pricing is very similar between their 26 gauge snap-lock product with 16" width and their 24 gauge snap-lock product with 20" width. On balance, it would seem that the 24 gauge 20" product would be a better choice.

Two questions:
1) Would one of those products have a greater chance of oil canning?

2) The builder has done a lot of 28 ga metal roofs, but has not done a standing seam. He is contemplating sub-contracting the job if he can find a good installer, but he might also do it himself. He is a perfectionist. Anything in particular that he should know re: installation difference of standing seam vs exposed fastener metal roof?

Thanks!
Ryan

With an ICF foundation and engineered trusses, I would hope the roof deck is straight!

The longest roof panels will be about 19ft long. It will be Vicwest Prestige roof.

Should I expect oil canning to occur without using ribs?

Should a backer rod be installed? Is there a bulge visible from the backer rod?

Thanks!