How to change material for a SM in gameplay woth multiple material options

Hi there.

I am exited to learn UE4 and acheive it’s best at architectural visualisations.
Could you please the kind UE4 developer community help me understand how to create a material menu something similar to this one Unreal Engine 4 – Loft in London Virtual Tour – Tech Demo [60fps][FullHD] - YouTube (go to 1:00 - 1:20)

I understand that the SM_Floor is in a blueprint and it has a collusion box around it to togle that button’s “Change floor color” visibility. How to create such a button so that it sticks to the bottom center of your screen while in gameplay? And how to create those different material options?

If you don’t have too much time to get into this. Could you at least give me keywords which to search or link to tutorial because I don’t know which keywords I should type in search.

Thank you. You are the best! Lets make it awesome!