This must be the cheapest way to create an extra room in a small terraced property. If you have a yard, think about roofing it using clear polycarbonate panels to create a light-filled space for al fresco dining even if it rains, to provide extra storage, as a space to house a washing machine and tumble drier to allow you to use your kitchen space better, as a space to dry clothes or as an outdoor bar for parties. The wooden window sills aren’t expensive and create a finished look that makes outdoors look like indoors. They can also be used as a bar top.