try not to take tuk tuk unless you are sure what is the fare and is game for bargaining.
taxi is a better way of travelling, second to their train.
i think you may be referring to the new platinum fashion mall at pratunam area.
it's air-con and house (supposingly) wholesale merchants, selling shoes, bags, apparels, stationery (only one, on the 4th/5th floor.. cant rbr now), watches etc.
if you are heading there, you shouldnt miss the pratunam shopping area where there are rows and rows of small shops selling cheap watches, apparels, shoes etc.
btw, recommend you take taxi there as the nearest train stn is quite a walk away (about 25-30min).
another plc to go for wholesale stuff is the chinatown, which you have to travel there by taxi too cos' no train stn there. tell the driver you want to go to "yao-wa-rart" (that's how you pronounce it). and if you shop there till night time, yes, that's the place to take sharks fin and birds nest. Look for Nam Shing or T&K Seafood.
Thanks Kai the info you provide is very useful