Using public transportation in Munich:
MVV site with tariff zones description and PDF map download:
http://www.mvv-muenchen.de/en/tickets-fares/tariff-maps/index.html
The MUC Airport is in the red zone, called Außenraum and the Messestadt is in the green zone called Innenraum.
The only one option that covers both zones is the Entire Network Ticket aka Gesamtnetz: http://www.mvv-muenchen.de/fileadmin/media/Dateien/3_Tickets_Preise/dokumente/TARIFPLAN_2016-Gesamtnetz.pdf
Messe München indications:
MVV Tickets prices:
http://www.mvv-muenchen.de/en/tickets-fares/index.html
MVV Ticket Shop: (for diy printed ticket)
https://ticketshop.mvv-muenchen.de/index.php/tickets
MVV App for mobile ticket and planning:
http://www.mvv-muenchen.de/en/journey-planner/mobile-services/mvv-app/index.html