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