Just add a trigger to the door ways, or one trigger to the main building, or a trigger to each building. When the player enters the trigger get player character → cast to myCharacter or whatever your character class is. then can fire function turn light on The function is on the character blueprint and simply accesses the light component and sets the enabled value to on. When the player leaves the trigger volume call function turn light off.
If you want to get a bit more fancy in your trigger blueprint expose a variable “turn light on” in the construction script. That way when you place the volume you can tell it if it should turn it off or on. Then just change up your trigger to call accordingly. So on trigger enter, branch turnLightOn = true then call function TurnLightOn. If false TurnLight off. That way the one trigger can be used all over your level and what or how it does can be changed based on what you set when you place the trigger as there will be a check box for TurnLightOn a check means yes, a blank means no.
Could keep getting more fancy but that will / should solve it for your base needs.