What are the requirements like height, weight, sight to pass the medical exam for getting a pilot's license ?
Are there any medical conditions that would make someone to fail it? I know daltonism would be one of those.
There are no height or weight requirements as far as I know and you dont need perfect vision. I wear glasses and have a "corrective lens" note on my medical. I think that at minimum your vision needs to be correctable to 20/20. See this link for some information as well as the information for doctors here. You can also get special dispensation for certain medical conditions.
On a small side note, if you are asking this in relation to a Private Pilot License, they may be doing away with the current third class medical regulations which will ease the regulations greatly.
All specific requirements to obtain a U.S. FAA Medical Certificate are listed in Part §67 of Title 14 of the Federal Aviation Regulations (FARs).
This part prescribes the medical standards and certification procedures for issuing medical certificates for airmen and for remaining eligible for a medical certificate.
It lists all specifications that have to do with the eye, ear, nose, throat, and equilibrium, mental, neurologic, cardiovascular, general medical condition and also any discretionary issuance.
To answer your specific question, you don't have to have a minimum/maximum height-weight to obtain a medical certificate. The operation you conduct and the company you conduct it with may have certain height-weight requirements.