[deltaten]

I aproach teak asI do decent mahogany. Didja ever hafta scribe a cabinet to a nasty, plaster wall?? Magnify by 10X and yer there! Ya (almost) can't do plumb and level; so ya gotta do square.. I'd establish a line right down the center of the space, then nX/Y axis offa tthat...Mark I eyeball after that.
Keep yer weight low and roundallathe corners. Oh!.and makesure the sole-to-seating height hits architechtural standards.nuthin' worse than feet not on the deck when seated! Other than that...have at it

 

[deltaten]

My pine mock-up worked so well I stained it teak and left it in place!

I generally use cardboard and blue tape.to "space-out" future cabs and such; just ta see if I'll fit.