I am Pakistani I want to marry a Ghanaian girl what is procedures

You just need your passport but your Ghanaian girlfriend will need a  birth certificate if she hasn't got a passport. Go to the registry office and complete the paperwork and then book a convenient time to do the actual marriage ceremony. You will need a couple of witnesses.
It will take you a number of years to get citizenship but you will be able to get a residents permit which you will need to renew every year for a minimum of 5 years before you can get an indefinite permit. You will also need a non-citizen ID card. Again you have to renew this every year. A spousal visa allows you to live in Ghana but it doesn't allow you to work here.

Hi.
Early last month I met a lawyer in Accra and discussed him this case along with some others.
He said it usually take 3 months for the foreigner to acquire Ghanian citizenship after marrying a local person.

I suggest you may be have been told this but if you look at the Ghana Immigration website you will find you have to have lived on Ghana for at least 5 years. Some immigration officers have just been sacked for operating a scam and giving permits illegally and those permits have been cancelled.  It is always better to do things the legal way and follow the correct procedures