Replacement Screw Diameter and Length Recommended

Hi, I've just bought a house with a 14-year-old trapezoidal metal roof on wood substrate. Many of the screws are rusted and simply spin in place when I try to tighten them. The screws are #10 x 1-inch. I'd like to replace these with correct replacement roofing screws. Everyone says, "Go one size up." Does this mean one size up in both diameter and length or one size up in diameter only? In other words, should I order #12 x 1-inch roofing replacement screws, or should I instead go longer and order #12 x 1 1/2-inch replacement screws? I can't seem to find the answer to this question anywhere, and if anyone could help me out I'd super appreciate it. Thank you.

Depends if they used the right depth screws before, but most often times...that means going up in diameter.

Great. That helps a lot. Thank you much.