My girlfriend want to buy a house with me on as a co-signer?

my girlfriend and her parent are looking for a house, due to her credit history she wanted me to co-sign i don't know what to do, should i co-sign then in 2 to 6 months have them deed me off it, what i don't know is if im a owner of the house or just helping with the loan, is there such thing like that or if im on the loan i should be part owner of the house or in other wards on the title of the house?