This is most likely the best place to go if you want a real tailored suit in Bangkok.
Went there in early january 2014 because of these reviews on TripAdvisor. Within only three days (during the beginning of Bangkok demonstrations) me and two friends had perfectly tailored suits and shirts made. The staff and Sunny always made sure we where comfortable, even offered us free bottled water or beer when waiting during the two fittings before the suits where finished.
Walked a bit around in the city before looking on TripAdvisor and would recommend avoiding the kind of tailors who has someone trying to convince you from the street (which Empire Tailors does not have).
Want tailored suit in Bangkok? Got to Empire Tailors!
When they have your measurements you can order new suits/shirts online.