How to I trim a store-bought rug to create a unique shape?

I would like to buy a regular rectangular area rug and round off one of the corners (can't buy this shape). Is there a good way to do this?

Although it is very difficult to get the kind of shape that you require in the market easily. For  this either you can give a customized order or you can do it on your own using a gardening scissor because their is not hand tool specifically for this. You can try and search outdoor living store to check  out whether you can get your kind rug or not. If you opt for doing it yourself than you should do it carefully and not hurt your self.