After some additional testing, it looks like query 1 is correct:

select s.suiteid, s.buildingid, s.SuiteName, b.buildingnumber, g.suitename, g.buildingID

from suites s

inner join buildings b on s.buildingid=b.buildingid

LEFT JOIN RealmStageSuites g on g.buildingid=b.buildingnumber AND g.suitename=s.suitename

WHERE g.suitename IS NULL AND g.buildingID is NULL

Anyone know what's wrong with Q2?