Most custom builders in Ontario will work out the price within the array of $150 per square foot to $300 per square foot. The majority of semi-customs are built at $200 per square foot, depending on size, design, systems, finishes, location, etc.he size of homes will certainly affect the cost of building a home. The larger it is, the more it will cost in total dollars. Having said that, the larger it is, the less it’ll cost per square foot.