What is the total distance? What are the planned winds? What are your alternates. Can you make it if you lost pressurization mid way?
Wen you have somebody like Universal plan for you, you are going to get the best route for the planned winds, and you get a very solid set of numbers to work with.
You can do it yourself, but I would like the peace of mind that it has been looked at by an outfit that plans these kinds of flights all the time.