Typical incubators in India gives $10000 for ~10%. Seed funding/Angel investing is very new in Indian context, so couldn't find much resources as reference. How to go ahead with amount/valuation.
If you go with the simplest method, I'd say you first need to understand how much you would need and how much he is willing to put in the company and then set somewhere between 10 and 30% for him depending on his day-to-day involvement in the company (which needs to be written down in a contract, of course).
But there is way more information needed to give you sound advice here, and still with all the info I wouldn't be the best one to ask. Probably someone from India would be better.