Can I build a diff myself, and anybody used this tool?

With the internet there is a wealth of information and visual aids that make doing this as a DIY project easier than ever - if you have the right tools.

Take a look at what tools you still need to get to do the job right and add up their cost. If you are "one and done" with the gear change you might be better off having someone else do it for you. However if you think you might be doing more than one gear change in the future it might be worth it to invest in the tools, learn how to do it, and save $$$ over the long-haul.