Though I read a lot about vegan substitute of cheese but I have not come across one that can be described as its perfect replacement especially in places where cheese is supposed to melt, like in Pizza. Does anyone has any experience with it ? Is it possible to make such vegan cheese at home ?
One thing to be aware of with many commercial vegans cheeses is that these work much better for melting over pizzas or casseroles if mixed with some additional liquid (eg by soaking the grated cheese substitute in some soymilk or soy cream and applying both together).
If looking to make your own meltable vegan cheeses, use recipes using plenty of fat and a combination of agar and tapioca starch as a starting point for experimenting.
Be aware that the mouthfeel of melted cheeses is quite a complex matter: It is more or less defined by a set of textures achieved at different temperature points (and probably the delay in texture change!) throughout enjoying a portion (which will cool down during doing so. Body temperature also plays a role here...).
Be aware that cheese melted over casseroles has a functional role in cooking them - once it is melted (melting temperature plays a role here..) it acts as a partial vapor seal, and probably also gives off or binds moisture/salt/fat.
Be aware that the melting behaviour expected of conventional cheese has regional subtleties to it: Somebody used to american-style processed cheese in these roles could be put off by the liquid separation/curdling/firming/hard stringyness effects you get from using natural cheeses, while somebody expecting the latter behaviour would probably consider the more homogenous result from processed cheese as mealy/stodgy/gloopy.
There is no perfect replacement for cheese made from plants, as cheese is made from caseine and other milk proteins that just don't exist in plants. That said, you can put your hopes to the Real Vegan Cheese bio-engineering project.
As it is now, you'll have to choose a cheese substitute based on your needs for the moment, for example whether it should melt or not. There are many vegan cheeses available in supermarkets (your mileage may vary, depending on where you live), and recipes are available all over the internet. A specialized facebook group like Vegan Cheese might be interesting to you. Here's a recipe for vegan cheddar cheese I just googled.