I Don't have any clips so guess you'll have to take my word for it but you can look me up on FortniteTracker - AkyyUK171974, i play with irl friends mostly but im pretty good. but these are the main buttons for building for me the rest is personal preference.
WALLS - MOUSE1
RAMPS - MOUSE2
FLOORS - FORWARD [FRONT BUTTON ON THE SIDE OF THE MOUSE]
ROOFS - BACK [BACK BUTTON ON THE SIDE OF THE MOUSE]
With the roofs i edit them to be downwards ramps so i can ramp up/down on the go without rotating.
F - BUILD MODE
I've got R3 [ RS i think if you're xbox] as C to crouch but also added E on the secondary list so i can reset edits with e and crouch with c.
Hope this helps as a base to build your setup on bro