Biggest factor, do you have kids and/or a dog. Redid my garden 2 years ago, removed water feature, gravel, relevelled , re-turfed, fitted sleepers etc, looked really good at first, two young kids and a dog later it can resemble the Somme.
Took a long time to do, weather and work mix don't let you have a good run at it, but I think it's worth doing yourself, cost wise, and the satisfaction is good, makes sure you keep on top of it if you've done it yourself too.
Just needs a good few things factoring in, time, cost (skips etc mount up). House opposite had theirs completely redone and new outhouse built, costs spiralled, workies didn't turn up etc, took almost a year and still doesn't look that good, ruined their front tok with diggers etc.
Plan it all properly first, as much as you can, but there'll always be hidden snags.