Buildwise, if you go Rod of Ages and get a Spirit Visage along with your hourglass, you usually shouldn't be dying too easily. Swain can still do nasty damage even if you don't go full damage, but its necessary to be tanky with him so you don't get blown up since his range isn't the best. For tankier people, a Liandrys Torment is pretty decent on Swain if your enemies continue to build HP like crazy. For roaming purposes, remember that Swain isn't very strong without his ultimate, and you should be cautious with your snare pre-6. Roaming depends on if your mid or top lane, since top is harder to roam from, but Mid is easier. Usually you'll only roam if your team actually needs help, otherwise if you win your lane, you should be able to 1v2 very easily.