i build easy using useful mods
but it works
if it's harder than you think , try to download these mods if you have pc
world edit:https://www.curseforge.com/minecraft/...

Construction wands for 1.16 or Better builder wands cause of 1.12.2 :
https://www.curseforge.com/minecraft/...
https://www.curseforge.com/minecraft/...


you need more colored blocks:https://www.curseforge.com/minecraft/...