Gosta Green is situated on the same site as Aston Uni, behind the main building and students' guild. It's the art and design faculty I think. It's about a 10min walk into the city centre. Aston Uni's campus is very green, plenty of choice for second year accomodation nearby.
Perry Barr is not a great area of Birmingham to be honest although you do have the OneStop shopping centre right opposite (huge Asda and loads of other useful shops). It's about a 10-15 minute bus ride into the centre of Birmingham and 20 minute walk to Villa Park (if you're into football!).