We added a build-only server, separate from the main one, where you can build freely.
Run /server build to go there. It's a separate world from the main server, so Lands (land protection), Jobs and similar systems don't work there.
Builds are protected with WorldGuard. Select two opposite corners of the area with the WorldEdit selection tool (wooden axe) and run /rg define <region> to protect the whole area. You can also invite friends to build with you.
See "Build server" in the Wiki for details.