300m^2 of roof! thats one big house Michael! do you live in a castle or something?
I found this out to not that long ago too, makes you think how much water falls on each and every block during a heavy rainfall and then goes down the drain. For example the old 1/4 acre block is just over 1000m^2 so for a decent rain event of 25mm thats 25 Kiloliters of water! enough for most households in Perth for a couple of summer months! but of course a house would look pretty ugly with a upside umbrella on it to catch all this water!