Using two types of dough (water and oily) will introduce flakiness in the crust. As air is trapped between the layers, there will be multiple layers of pastry making for a crunchier and lighter bite. There are different ways to roll out and prepare the dough. It can be hard to show you exactly how my Mum did it but once you understand what is being achieved here, you will get confident and find different ways to roll it out.