The paint scheme is stainless steel sides and gray roof. I was thinking paint the whole thing with the metallic paint, then mask and do the gray. But I recall reading something about metallics going on last. Then again, it could have been metallics first. Who's on first? What's on second?
I generally do metallics first, unless there is a lighter color in the scheme. Always lay the lightest color first. Honestly, with the roof being a different color, either one could be first. Just be sure to mask the other color areas (roof, or sides; depending on what you paint first) well.
Do it in such a way you do not have to mask or tape the metallic as it will often pull. And, You can paint light to dark or dark to light....does not matter. Some colors are more prone to pulling off with the tape than others and that should be the deciding factor.