  We generalize Conway-Sloane's constructions of the Leech lattice from
Niemeier lattices using Lorentzian lattice to holomorphic vertex operator
algebras (VOA) of central charge 24. It provides a tool for analyzing the
structures and relations among holomorphic VOAs related by orbifold
construction. In particular, we are able to get some useful information about
certain lattice subVOAs associated with the Cartan subalgebra of the weight one
Lie algebra. We also obtain a relatively elementary proof that any strongly
regular holomorphic VOA of central charge $24$ with a non-trivial weight one
subspace can be constructed directly by a single orbifold construction from the
Leech lattice VOA without using a dimension formula.
