Here is a link to a good review on Raman spectroscopy of graphene.

http://www.nature.com/nnano/journal/v8/n4/full/nnano.2013.46.html

Optical microscopy is the easiest if you have some experience: you can observe the graphene growth directly, for example, after it is grown in Cu, you just oxidize the Cu and the parts with graphene will not oxidize. Then you can use the microscope and see the different layers formed.

I would strongly recommend though to confirm the number of layers by a complementary technique, such a Raman microscopy.

please tell me how we can determine the layers by using raman spectroscopy..have you any idea about on that.

Here is a link to a good review on Raman spectroscopy of graphene.

http://www.nature.com/nnano/journal/v8/n4/full/nnano.2013.46.html