If you MUST buy any USA Mags. First go and measure the roof your home for square footage.
Then Decide if you want 20 or 30 round USA Mags. I think 20 rounders are easier to work with.
OK now you have the square footage and the size of the MAG you want.
lets use round numbers.(I am a bit slow)
A = Roof sqft
USA 20rd Mag = 2.5"x7.5" x SQ ft
Total Number of USA mags = B
Purchase supply of USA Mags = to B. [You should have no problem finding most in junkyards or trash can]
Then line all the USA Mags up flat unloaded in the road in front of your house and wait.
As the cars and truck come by they will flatten the USA Mags one by one. As I have done more than once.
Remove the pancaked USA Mag bring it up to the roof and nail it on in nice neat rows. When all the USA mags are pancaked and installed you will have a nice metal shingle roof.
The roof should last if painted properly over 50 years .
This is the only use for any USA Magazine I have ever used or seen.
USA magazines