Please advise on this trigger function

Good day,

I have two tables, table1 & table2 with two trigger functions set on
table1, on before & after insert. table1 contains a foreign key reference
to table2, called building_id.

when a row is inserted into table1, building is in text format, I need the
after-trigger to lookup this text value in table2, if it exists, retrieve
the id & update table1 with it, else if it doesn't exist insert it & update
table1 with the new id.

I could do this in the before-trigger, but how do you rollback the newly
created row in table2 (if it's a new value) if insert failed on table1.

my problem is passing values between the before & after triggers, I could
retrieve all the required columns' values in after-trigger using NEW.* but
what about building_id? I could set it temporarily to NULL in
before-trigger because clearly the foreign column cannot accept a
textual-value, then do the lookup with table2 in after-trigger, but how to
sustain the original building textual value?

Thank you.