How do I prevent players from building in the zone spawn?

Use /PerBuild (for entire world) or /Zone (for an area.

 

Example: /PerBuild level Operator

 

hope this helps.

/zone add Spawn <rank> (for example nobody)

then mark the area either by breaking the blocks or doing /m

 

if you're on an os map, you should do /os zones add Spawn <rank>

do /Zone Add Spawn Rank i would perfer co owner