Decking  and exterior work - strictly for fair-weather days! For decking projects you typically need to allow around £100 - £140 per square meter fitted, assuming a treated softwood single-level deck laid on treated softwood bearers, though obviously variations on this will affect the overall cost. For garden studios and summerhouses, the cost will vary depending on the specification and finish, but think in terms of around £2.5 - 3k per Square metre, all-in.