Yes, you can have a round UPVC window if you want, the type of window you choose depends on your personal preference. As well as round windows, you can also choose semi-circular windows for above your door.
The manufacturing process for making UPVC Windows is highly flexible. The material that makes up the frame - the profile - is extruded UPVC, which is a plastic that can be moulded into many different shapes while also being completely rigid when set. This means that the fabricator who makes your frames can create many different shapes to fit the design of your home.
It is important to note that a circular window may cost more than an equivalently sized square window due to the increased work that is required to build the frame and to shape the double-glazing panel that will fit inside it. Your installer will discuss your design with you in detail and help you to choose the perfect frame style to complement your home.