Generally hire specialist trades for anything inside. Whatever the job, they can always provide a better finish and in half the time. Plus, it's good to give local people work when you can.
Some things I do myself, usually basic repairs on anything without a plug or tap attached.
I find anything with timber I do myself but that's because I have been a hobbyist woodworker for a time. I always do the garden myself, but anything like driveways or paving, I tend to hire.