To begin with Siam Square.
Located off Siam Square station on the sky train. Siam Square refers to the collection of small boutiques located opposite Siam Discovery and Siam Paragon. Siam Square was trendy shopping area 50 years ago, and it remains one of the trendiest shopping areas today. These small boutiques are where the actual locals shop predominantly colleges students from Chulalongkorn University and the young professionals working in downtown Bangkok. You will have to brave the outdoors as you flit to and from each store, and nothing there is particularly cheap. However, this is where you go to buy one or two nice things for yourself as opposed to the cheap tee-shirt you are getting for your second cousin twice removed.