Do i include any existing, untouched, parts of the home in the estimate of sq metres for costing purposes ? What is an average price per square metre ? The home is a wooden free-standing cottage built of wood in inner-west sydney

multiply length by width of said structure..that is your square meters… this is called "floor space they not wall space….if you want wall space..you measure each wall(usally 4 walls will be same measurement) heighth X length is the formula….total all walls if it is wall area you need…then add them together..the cost per sm..well that totally depends on what you are going to do with it..differnet paint finishes, floorings, tile etc..good luck