Tawseef - I think that you should not wait for an invitation to write a book chapter. Search the internet for "Call for papers/book chapters" in your discipline or allied disciplines. Also, ask your seniors/colleagues/scholars for help.
I once contacted a senior Professor from a reputed university and requested him to send me "Call for papers/book chapters" if he was in touch with authors, editors or publishers. It worked and later on, I received a good number of invitations.
Thanks for your kind reply sir. I hope this will help me out as i am student if plant sciences. If you are somehow related to my specialization then do help me out. Here is my email ID [email protected]