You can use the oneline xONEx (Oneworld Explorer) tool to build your desired itinerary; just ignore the errors and don't rely on it for validation. Then check here or with an airline (e.g., AA RTW desk) to see if it's valid. The advantage of using the tool is just that it's a handy way to select the flights, manage connection times, elapsed days, etc. If you call the AA RTW desk you can just rattle off the cities, dates, and flights, which saves a lot of time with the agent saying "I have a 5:10 AM, a 7:30 AM, a ...."