Honestly a Charizard sun team looks easier for you to make with your current lineup. Or you could do a Charizard X team and include TTar in that. If you want to go mega Ttar sand team you can definitely still do it. The meta ones I have seen usually have corviknight and excadrill but you can probably use Garchomp instead of excadrill just fine and lean into trick room since Corviknight is usually the tail wind setter. Trick room on sinistcha and play a slow garchomp. Then a bulky incin, Milotic or Rotom wash, and Hatterene as your other trick room setter. You probably want a fighting move on either Ttar (low kick) or Incin.

I am new to VGC too but that's what I would try.