Re: metal roof - paint or replace?
If this is a corrugated metal roof, the silver paint will do, but if you have standing seam metal, never use silver paint or any kind of other mobile home roof coating product on it! Standing seam "terne" metal roofs are very thin and don't take well to the modern chemical brews that roof coatings contain. It will lead to worse problems.
A terne roof is a lifetime investment, but if it has begun to fail to the point where it has pinholes, you're better off re-roofing, otherwise paint and enjoy.
The old standard paint routine for terne was very lengthy: wash, wire brush and scr ape; prime with "Tin-o-lin" red oxide primer, then coat with the oil finish coats. Very time-consuming.
The new method consists of the washing and wire brushing, and the use of a phosphoric-acid type rust converter, then directly apply the acrylic roof paint. If you have a lot of surface rust, you may get 2-3 years out of a paint job before the rust starts to bleed through. DAMHIKT.
Remove not the ancient landmark, which your fathers have set.