You can get a +6 without spicy stew. First, outfit your kitchen with teak shelves 2, as well as some kind of sink, stove, and larder. Take some tea leaves from your larder and a kettle, teapot, and cup from your shelves. Fill the kettle with water and boil it on the stove. While it's boiling, put the tea leaves in the teapot. Once it's done, take the kettle off the stove and pour the water into your teapot. You will now have 4 doses of tea that you can drink from your cup. This boosts your construction by 3. Also, you can do the quest The Eyes of Glouphrie and get a crystal saw which lets you build things up to 3 levels above your current level. These effects stack, giving you a net +6.