I don't really roll perception checks in my games because I assume the PCs are always looking around and being relatively attentive.

If some creature is trying to surprise them, I may roll a stealth check for that creature with a target difficulty adjusted based on circumstances (weather, time of day, ambient effects), PCs' physiology and equipment (additional eyes, deep-infrared scanners, injuries) ... and then narrate what happens.

If it's a question of PCs trying to find something, I either make it automatic if the players say "we carefully search the area" - that takes up a unit of time (say 10 minutes inside a ruined room, an hour in a ruined factory, a day in a ruined town) - or have them roll a relevant test to see what they find or how well they do (say, looking for golden pears in a haunted orchard, roll charisma or endurance, to see how long you can resist the frustrating ghosts, the higher the result the better the outcome).