Hello,
I am kind of new at Unreal Engine 4 and I was wondering if it was possible to make a base building feature for a game, where you could scale certain types of objects to create different sized walls, floors, roofs, etc.
Yep, you can do that in your blueprint with a “set scale” node 
Just create an actor bp - add a mesh - get a reference to your mesh in the event graph - “set scale”
I think I did what you said, but how would I know if it works? Do I need something else to test this feature out? Sorry for these questions, I’m a beginner at this and I couldn’t find tutorials anywhere.
You need an event that activates those nodes -> e.g when the player presses “1” (when you do the event in your actor bp, make sure to also add a “enable input” node which should get activated at the start)
Yeah that’s getting there.
If I was doing this I’d probably do something like so.
Depending on what your exact goal is you’d need to modify this of course but this should get you started.
You don’t really need to enable input every time you press the button, only when you need it to be active.
In this case I set it on begin play, but maybe if you’re making a base building game you might want it only when you have the building selected.
Also doing something like scaling up by 1 exactly might not be best, you could make it relative by multiplying or maybe just do smaller intervals.