When you create table in Web UI - you can enter schema field by field ( mode - default mode) or you can enter schema as a text (Edit as Fields mode)Edit as Text
See more about creating tables with different clients (in We bUI section above option is not presented, so that's why you missed it I think)
P.S. As of today, BigQuery doe not support DDL - so is not availableCREATE TABLE
Update
As of today - Jan 17, 2018 - BigQuery support is now in data definition languageBeta