I also agree with everyone for the most part.
I don't think there's a problem with creating a recipe from scratch for your first all grain brew, but that's only if you've already created tons of recipes from scratch for your extract recipes and have a pretty good grasp on how the process works, even if you haven't done all grain before. If you've mainly been using kits or other people's recipes so far, then I definitely wouldn't start creating your own recipes with your first all grain.
I also agree with others that I probably wouldn't do a super high-gravity beer as my first all grain. With extract, you can just pour in as much LME and DME that you need, but with all grain, there's issues with brewhouse efficiency, and you won't know what your normal brewhouse efficiency is, plus higher gravity beers tend to have lower brewhouse efficiency, so it might be better to start with something in the 4% to 6% ABV range (just as a general idea) and try the double or triple IPA a bit further down the road.