What you ask is just the way of doing shcemas theory in

http://books.google.it/books?id=RDKRyP00aoMC&printsec=frontcover&dq=demazure,+gabriel,+algebraic+geometry&source=bl&ots=bIOMOQ4o5w&sig=gKU-IBBnUqR-1nMu9tV3p5fUjDE&hl=it&ei=zLfuTNLPHsucOuL7pfwJ&sa=X&oi=book_result&ct=result&resnum=1&ved=0CB4Q6AEwAA#v=onepage&q&f=false

What you ask is just the way of doing scheme theory in

Demazure and Gabriel, Introduction to algebraic geometry and algebraic groups. Translated from the French by J. Bell. North-Holland Mathematics Studies, 39. North-Holland Publishing Co., Amsterdam-New York, 1980 (Google Books, MR563524, zbMATH)