For my buyers that wish to build their own home, I will contact the City of Vancouver to find out what the property setbacks are, if there are any by-laws governing what is allowed to be built on site, whether there is a lane dedication, can a laneway house be built, if a property is sub-dividable and etc.
The general rule of thumb for maximum finished area a 2 level house can be built on site is: 20% of total lot size + 1,400sqft (E.g: Standard size lot of 33×122 will allow 800sqft + 1,400sqft giving a total of about 2,200sqft) For 3 level houses (a.k.a 2 level + basement), it is 70% of lot size (E.g: Standard size lot of 33×122 will allow an approximately 2,800sqft 3 level home to be built on site) This is a general rule of thumb for approximate calculation, I still consult with City Hall on maximum buildable size as sometimes there are other restrictions like what is allowed above gradient.