How do I have an object fade in and out?

I am trying to set this up in the event sheet where the player enters a building and the side would fade out allowing them to see inside and when they exit it fades back in, but when I attempt this the fade just goes in a loop. Sorry if there were any posts about this before, if there were any I couldn't find them.

Something like that ?

Yes

How would I make an event sheet like that?

I'm not sure what you mean. Perhaps you should do some tutorials before starting your own project ?

You can read the Beginner's guide to Construct 2 or How to make a Platform game.

As in what would I insert into the event sheet to make an event like this. I have done multiple games before but the logic behind this really confuses me.

Still not sure what you're asking for, maybe because this sheet it seems pretty simple to me.

I first test the player X position regarding the building. If the player is between the door coordinates and the right building coordinates, then it sets the building variable "fading" to 1.

If this variable is set to 1, it decreases progressively the building's opacity. If "fading" it is set to 0, the building opacity increases back to 100.

Of course there are many ways to achieve that, and some are better than mine. Still, it's a simple way to do it.