Ask for opinions about reputable tailors and tell them exactly what you want. The shops will have books of patterns and designs you can choose from. A lot of good tailors are located on Sukhumvit Road and near riverside hotels such as the Oriental. I paid about 120 baht for a tailored skirt. Men's suits are a good deal too - a good custom-made suit costs about $200, and a custom-made shirt about $40. World Group Ltd. on Charoen Krung Road near the Oriental is especially good.