Yeah, DungeonDraft is a top choice, and it's cheap and a one time purchase. Inkarnate has some decent features but you'll have to subscribe to get the full featureset. Other World Mapper is okay for it, that would be my choice if I wanted a program that does regions and cities too, since you have to get Wonderdraft if you want to do regions and they don't have a Citydraft, heh. But you use Photoshop for those kinds of maps. So, DungeonDraft would be my suggestion.

But you CAN use Photoshop for the purpose. You could just use Photoshop's grid, set it up to the appropriate grid size and use snap to grid. You can set up things like layer styles that would serve as outlines for walls and whatnot.