Hello okie: The Y quad beam antenna might be slightly effected by the metal roof. If the antenna could be higher that would be better.
Hello Okie. I have a model of the Maco 103C antenna that I setup Vertical.
I also have a modeling object that I made, a metal pitched roof 17'H x 30'L x 38'W.
I set this vertical M103C model on a mast connected to the ground and 2' feet from the building at its peak. The bottom of the vertical elements are about 7.5' feet above the 17' foot roof peak.
Note: these models do not necessarily represent what will happen at your location.
I think Jay gave you a reasonable expectation in answer to your question and I see the models below in support of his suggestions.
Models in the PDF file below.
1. shows the starting model, a vertical Maco 103C with no metal building.
2. shows the beam 2' feet from the metal roof of a building and pointing North over the roof top.
3. shows the same view as #2 with the beam pointing South away from the metal roof.
4. shows the beam rotated 90* degrees pointing to the East.
As I rotated the antenna in these three directions I noticed the feed point match changing. So, I tweaked each model a bit to make for an improved match. On rotating your antenna in this situation...you might expect the match to vary as you rotate.
I will also do the horizontal version later just as Unit 75 suggested, and see what modeling might suggest there as well.
Again, I think Jay is right.
Okie, keep us posted on your progress.