ok so your house is 20 yards wide, that akes care of one side
if you have only 20 yards of fencing then hmm
the way to max the space is to make all side equal
20 is for 3 sides
20/3=6.6666666 per side
assuming you don't need to fence the house side
the amount of fencing is 6 and 2/3 by 6 and 2/3 by 6 and 2/3 yards