Male Maine Coons are often larger than females, but the overlap between individuals means sex is a poor substitute for measurement. A large female may need more sleeping space than a smaller male, and neither should be encouraged to gain excess weight to meet a breed stereotype. If you are choosing a kitten, ask about the parents and expected development, while accepting that an exact adult size cannot be guaranteed. Keep equipment decisions flexible as the cat grows.
A carrier should remain comfortable and securely rated for the cat's weight, and a perch should offer enough surface for the actual sleeping position. Adult body condition is equally important. If you are unsure whether your cat is simply large or carrying extra weight, ask your veterinary team to assess them rather than comparing them with impressive photographs online. Compare a kitten's measurements across several months rather than ordering everything from a predicted adult weight supplied in an advertisement.
For product comparisons alongside this advice, see Velvet Nest and Sterling Court litter tray. The details below explain their sizes and uses.
Further reading: gccfcats.org; pdsa.org.uk.
Velvet Nest
Sterling Court litter tray
Taj-MeowHall