@ sp (at) Elara, i would highly recommend the san remo 210 by champion homes. It suits a 12.5 metre frontage. I have friends who have built on a similar sized lot (350-370ish) and this design suited the lot reallly well. The starting price of these house for a full build package with all the bells and whistles is about $250 000-$270 000.
Here's the link: http://www.championhomes.com.au/home-designs/san-remo
Another house i think woukd suit your lot is the eden brae home oxford 23 that suits a 12.5 metre block. The starting price is about $250 000.
Here's the link: http://edenbraehomes.com.au/a/55.html
Hope that helped! Good luck with the building!