1981 cutlass supreme 3.8 (lost 5q oil)

I recently rebuilt my 81 cutlass supreme 3.8 v6 at my school, and lets just say they dident do that good of a job. but when i got it back tey told me the engine and tranny was done and good to go. I finished up the buttoning (timing spark plugs etc.). And when i started the car up it ran fine except for the exahust sounding like it was never put on. Then about a min or two later all the oil in the engine poured out into my driveway. any thought why it happened??

Poured out FROM WHERE??