Offer Letter For A Consultant

I am in a process of Hiring a very experienced old person as a consultant on contract basis for our company who can advice and contribute his valuable ,experience in the decission making of the Marketing department nationwide.
Please help if any one have any draft or sample offer letter which can guide me the main content for the duties and the main things one has to be in consultant offer letter.

Dear Fawada,
I am expert in drafting the agreements. I do conduct the training on Business Writing also. Occasionally I write articles and these are published in print or electronic media.
I will help you, however, my services are paid one. You may obtain consent from the authorities concerned of your company to take the matter forward.
Thanks,