I would never co-sign on a loan unless I was prepared to make the payment myself for the duration of the loan. Which could be up to 30 years in this case.
If you are looking for a co-signer they have to be comfortable with relying upon you to make consistent, timely payments. Likewise if you are planning on being a co-signer you may want to make certain that you are in a position to absorb any consequences such as late payment and the reduction of future mortgage credit available to you.
There are no negative effects to credit when co-signing on a FHA loan if the mortgage payments are made consistently on time. However, it is important to know that unless you are related (family), you are unable to co-sign on a FHA loan.