will streching your arms out after lifting weights affect the building of muscel?

Answer 1

No it won't.

When you're lifting, your muscles get tiny tears in them. As those tears heal, your muscle grows. The use of your muscles causes lactic acid to build up. Stretching does help the body remove lactic acid from the muscles, which is what causes you to be sore.

Answer 2

stretching all muscles prior to and after a workout provides them with greater efficiency and opportunity to grow, strengthen and eliminate the potential for injury.