I understand the frustration of spending time to build your buildings only to come on the next day and see it griefed. How annoying! Thankfully staff has a way to rollback block damage, but we use plugins that make it so staff doesnt need to get involved! On the Survival Server we use the GriefPrevention plugin. To get started the easiest way is to type /claim. You can also drop a chest, or use a golden shovel in /kit claimwand. Anything inside the protected area will be safe from damage! To add friends to build, use /trust <player>. To delete your claim, use /abandonclaim Easy! Edit: the Creative Server is offline for foreseeable future. On the Creative Server we use the PlotSquared plugin. Simply stand inside an unclaimed plot and type /plot claim or use /plot auto to have it find an available one for you. To allow a friend to build on your plot use /plot trust <player>. To delete your plot use /plot delete. Easy! Staff may not rollback any griefing that is not in a protected area! Be sure to protect anything you care about! Edit: We've made claim blocks free! Check out this post: Changes to claim blocks!