The sheet builder will always build the smallest unit cell for the selected chiral indices. But of course, all the (n,0) and (n,n) cells are equivalent (just repetitions of (1,0) and (1,1)). As always, computing a repeated structure has no real influence on the results except to make the calculations longer and results harder to interpret due to zone folding.
I would say the main purpose of the sheet builder is to quickly generate large surfaces of graphene that you can use to cut out shapes etc.
The Nanosheet builder is quite well tested, so it would be interesting if you could let us know exactly how to make it show error messages, so we can fix it.
