Quantum-mechanical calculations of electron magnetotransport in graphene Fabry-Perot interferometers are presented with a focus on the role of spatial structure of edge channels. For an interferometer that is made by removing carbon atoms, which is typically realized in nanolithography experiments, the constrictions are shown to cause strong interchannel scattering that establishes local equilibrium and makes the electron transport nonadiabatic. Nevertheless, two-terminal conductance reveals a common Aharonov-Bohm oscillation pattern, independent of crystallographic orientation, which is accompanied by single-particle states that sweep through the Fermi energy for the edge channels circulating along the physical boundary of the device. The interferometer constrictions host the localized states that might shorten the device or disrupt the oscillation pattern. For an interferometer that is created by electrostatic confinement, which is typically done in the split-gate experiments, electron transport is shown to be adiabatic with Aharonov-Bohm interference observable only at some ranges of magnetic field, with interfering path going through depletion regions. Interference visibility decays exponentially with temperature with a weaker dependence at low temperature.