Theatre books are on the third floor of Armacost Library.
Since the library uses the Library of Congress classification system, most theatre books have call numbers beginning with PN.
Use this map of the library to find your way to the theatre section.
The Library of Congress classification system reserves the call number range from PN1600 to PN3307 for scholarly books on theatre history and criticism, technical theatre, and theatre design.
There is no special section for play scripts; they are grouped in with prose fiction, poetry and other creative literature and organized according to the geographical origin of the language the play was written in. Here's a partial list:
PA: Classical Greek and Latin
PK: South Asian
PL: East Asian and African
PQ: French and Spanish
PR: English - Britain and former colonies
PS: English - American
See the section "Academic Books and the Publishing Process" in the Introduction to Library Research in the Arts to learn more about how books are published.