Go into your StarMade folder and find the server.cfg file, right-click and edit it with Notepad++, Notepad, or any word program (I recommend Notepad++ if you have it). Find "PLAYER_MAX_BUILD_AREA = 10 //max area a player may add/remove in adv. build mode" and change that 10 to any number you like. Save, and you're good to go!