Typically, you find out how much build you receive for the previous event when you get your character sheet at the beginning of the current one. That said, here is the basics of it below, copied from the relevant webpage.
At each event, you can earn a maximum of 8 build, not including SVP transactions. Additionally, build earned is awarded after Events not during an Event.
1 – pay for at least 1 Period
+1 – pay for 3 Periods
+1 – Role-play/Combat Build**
+1 – NPC Shift (min. 4 hours)
+1 – Kitchen Shift (min. 4 hours)
+1 – Complete a clean up assignment at the end of event
+1- A second point for clean up if you stay till the end.
+1 – Bonus Build – $10
**1 build will be awarded for roleplaying and combat safety. This build is automatically awarded to every player unless the player gives staff reason not to award them this point. Reasons would be; not role-playing at all, non-appropriate costuming, flagrantly talking out of game at in game areas, etc.
"The End to War, the End to Pain,
these will come in Seventh's reign"