you know one thing about using rocks for home wall holds is that they get COLD. in the winter when the most serious training time is, if your home wall is in a garage or basement, they might be so cold as to be painful to pull on. even the rock holds in a gym i used to work at suffered from this problem.
wooden holds dont feel nearly as cold during cold temps. also if you buff them up supersmooth they become incredibly hard to use as footholds and hard to use as handholds which is good for training technique on.
its easier to customize wood than stone anyways cause you ca use regular carpentry equipment instead of masonry equipment.