I am a newbie looking for a cheap to build coop design for my 6 Black Australorps that can be secured against New Hampshire critters (fox, bobcat, fisher cat, racoon) and can be heated for our freezing New England winters. I am thinking of a 'tractor' to move my ladies around the yard. Maybe that's not necessary if I can move a run around the yard instead? Any design suggestions will be much appreciated! thanks in advance!