Presume you mean "skylight"? This term is a little vague and could mean anything from a (Velux) proprietary rooflight to patent glazing or a polycarbonate rooflight (usually found on flat roofs). Can you give me more information? Is the roof flat or pitched? Velux rooflights are a good, inexpensive rooflight and are available from most builder's merchants, complete with flashings to suit the roof material. Patent glazing is an expensive option and is generally made to order; considerable builder's work or attendance may be required depending on the design etc. Polycarbonate rooflights (Coxdome is the market leader AFAIK) are a simple solution in flat roofs, but Velux have a new product suitable for flat roof installations on the market now.