If you plan on being an engineer, you should probably already be a miner. Miners collect ore and smelt ore into bars to create the majority of engineering items. Engineer recipes often include jewels, which are found in a variety of places. Typically, most engineers buy or are given rare jewels from other players. The auction house is a good place to buy gems if you can't mine them yourself. Some engineer recipes require leather, which you will need to buy from a skinner or the auction house. You will need to find a lot of other odd ingredients for your recipes that might need to be purchased from other players. Some items can actually be fished up with the fishing skill or found from monster drops or treasure chests.