You can access the U.S. State Department's adoption website below. It provides authoritative information on adoption from various countries, but this is the section on Ghana:
Ghana.
As you will see from the website, one must be resident in Ghana for three months in order to proceed with an adoption, unless a Ghanaian court grants a waiver. This rule makes it difficult for families to adopt from the country, and limits the willingness of agencies to work in Ghana. However, other requirements appear fairly manageable. Ghana is not a party to the Hague Convention, so if you are an American, you do not need to work with a Hague-accredited agency, and you would use the I-600A/I-600, instead of the I-800A/I-800 for immigration requirements.
Do be aware that the child you adopt must meet the requirements of the U.S. Immigration and Nationality Act in order to qualify for a visa; in short, the child cannot have been living with two parents. He/she must either have been living with a single parent who cannot support him/her at a level considered normal in Ghana, orphaned by the death of both parents, abandoned by parents who cannot be located, removed from parents who were deprived of parental rights by a court of law, or legally relinquished to an orphanage with no further contact.
Sharon