So I've about finished with making an infiltrator style character for a campaign, but I wanted to make sure my understanding of stealth is clear after my last sneaky character was largely useless.
Stealth requires you have concealment from the target, correct?
Stealth requires that you be unseen. Typically, this means invisible, or behind total cover, or in a space that is totally concealed. A blinded enemy can't see you, either.
When outside of combat, how does stealth work without cover?
It doesn't - if you can be seen, your stealth breaks. If you move while stealthing, you must remain unseen from those you are stealthing from. Whenever they get line of sight, your stealth is over.
Invisible rogue, sneaking past guards when he walks into an antimagic zone. Is he immediately revealed, or is he allowed a stealth check? What if it's at night?
If the invisibility is stripped off, he's immediately revealed. "At night" isn't enough concealment to be unseen typically. If the guards were blinded or if the rogue was behind a wall or something, though, the rogue could keep stealth.
During a bright day, a rogue tries to hide on a roof to wait for certain targets to pass by in the street below. Can he hide on the edge so he can see down, or does he have to break like of sight completely so he can't see the road in order to stealth?
Basically a DM judgement call - if the rogue can be seen, stealth ends. I'd probably allow a rogue to stealth in this circumstance with the usual trust that most folks don't habitually look up on roofs, but if the enemies are expecting an ambush or something, I might rule differently.
I have a feeling my GM was ruling stealth a bit incorrectly, but wanted to check. I enjoy playing stealth characters but my GM said I'm not very good at them. What happened in those cases was no stealth allowed, guards were instantly alerted. And in the ambush situation, I had to move to the center of the roof so I had total concealment and wait for the party to signal me that it was time to strike. But I see elsewhere that stealth is apparently different in and out of combat, so I need ruling help.
The big things is that
if you can be seen, you cannot be hidden. Sometimes, the rules are explicit about if you can be seen - you can be seen in dim light, for instance. Sometimes, the situation is a bit more up to DM judgement - are the guards distracted and talking among themselves so they don't see you sneak up behind them? Maybe. The DM ruling wasn't wrong in either situation, because if someone is looking at you, you aren't hidden from them.
The DM's judgement call is whether or not someone is looking at you when it's ambiguous.