I think in your situation, they could be referred to 不肖的/無賴的/流氓的 建築工/裝潢工/水電工，these are common names for the group of people you described, but I would suggest that you could rephrase it to 我不滿意工人們的施工品質和工作態度 (I'm not too satisfied with neither the traders'quality of work nor their work ethics/attitudes.)

1.cowboy 牛仔 or 牧童 but 牛仔 usually means adults or adolescents and 牧童usually means children.2 2.rogue trader i think it's a film ,which is tranlated as in chinese《巴林银行倒闭案》.obviously,it isn't be translated literally. and 流氓,无赖,痞子 means rogue. 商人,操盘手(use in equity market) means trader. 3.builder 建设者,建筑工(whose job is to builder houses) you should know that builder can express建设者&建筑工.but 建设者 can express the man who create or lay foundation of something abstract or concrete.BUT 建筑工 only means house builders. ex:爱因斯坦是相对论的建设者. Albert Einstein is the builder of Relativity. and "建设者"in this sentence is abstract 4.plumber 管道工,but as i know, in american slang,plumber also means the people who prevent the intelligence to be leaked.now here,we just discuss the general meaning. 管道工 is a person whose job is to connect and repair things such as water and drainage pipes, baths, and toilets. Apparently,rouge is dangerous.And all the rest people do real work hope it can help you^_^

I think you'll find the term is 'rogue traders'. 'Rouge traders' sounds like they're make-up artists selling contraband blusher....