http://cs.elderscrolls.com/constwiki/index.php/Creating_a_House is your friend Use Ctrl-F in Firefox and type in Hand changed to zoom to the section where its described. Looks like a nice tutorial actually...

.....All it says is "The other two check boxes, 'Force Hide Land' and 'Hand Changed' won't affect your house, as both of these control cells of the exterior world with terrain. Leave these both unticked."
Can you please explain it to me?