how much class object occupy memory in heap..?

It depends on what you mean by space in heap; the MSDN thread that Suthish refers to indicates that there is not a clear answer to that. There are circumstances in which the question ("space in heap") is relevant and in which there is a meaningful answer.
 
Also, the phrase "make second object" is vague. It depends on what you mean. Am I correct that a class object is a reference type? I apologize if I am confused. If you make a copy of a reference type, then only the reference gets copied, correct? So it depends on what you mean by "make second object".

what is the size it will occupy I don't know but whenever you declare any class or object it will not occupy any space it will occupy space of memory only after initializing means whenever you call that class or object then only it will occupy the space of memory.