How do I clone something to the coordinates of a player?
Solution 1:
/execute at @e[type=item,nbt={OnGround:1b}] run clone [pillar corner xyz] [pillar opposite corner xyz] ~ ~ ~
and then on a chain conditional command block,
/kill @e[type=item,nbt={OnGround:1b}]
This will spawn a pillar on any item that you drop and then delete the item. I'm sure you want to be more specific with what items to spawn pillars at, but you haven't specified, so do as you will.