Single crystals of the layered organic-inorganic perovskites, [NH2C(I)=NH2](2)(CH3NH3)(m) SnmI3m+2, were prepared by an aqueous solution growth technique. In contrast to the recently discovered family, (C4H9NH3)(2)(CH3NH3)(n-1)SnnI3n+1, which consists of [100]-terminated perovskite layers, structure determination reveals an unusual structural class with sets of m [110]-oriented CH3NH3SnI3 perovskite sheets separated by iodoformamidinium cations. Whereas the m = 2 compound is semiconducting with a band gap of 0.33 +/- 0.05 electron volt, increasing m leads to more metallic character. The ability to control perovskite sheet orientation through the choice of organic cation demonstrates the flexibility provided by organic-inorganic perovskites and adds an important handle for tailoring and understanding lower dimensional transport in layered perovskites.