It can be an ordinary tree, plastic, as well as a stone, no matter what it is — natural or artificial. Also easy to do for this and such materials as chipboard and MDF. The main function of the windowsill is to prevent the fact that the condensate of your apartment, which is formed on the window products of your apartment, does not occur on the walls and gender of your apartment. But not every person acquiring a windowser of stone understands that he not only cannot perform his direct functions, his direct duties, but performs a decorative function. So its content in the apartment does not make sense, since its cost is high and unjustified.