Keller make a very good ply shell. Just like most companies that don't build shells into a finished drum, & therefore don't test them as a finished drum, they sometimes get inconsistencies in their product. Vaughncraft make steam bent shells, & they too have had quality wobbles over the years. Steam bent shells are much more difficult to build than ply shells, & also exhibit very different sonic properties to their ply cousins. A
well made steam bent shell will generally out perform a ply shell, but only if every aspect of the finished drum's design is cohesive & considered. Joshuah Tree Percussion, amongst others, offer stave shells for you to complete your build. Same applies to stave as it does steam bent, in terms of quality requirements of shell, eventual build, & potentially superior results.
Essentially, you get what you pay for. The majority of custom drum companies use shells from the three manufacturers mentioned above. There are other suppliers of raw & semi finished shells too, but remember, both custom companies & larger manufacturers who buy these shells, have years of experience in finishing them. This means that not only are they in a better position to finish them appropriately for the sound character they're after, but they're also better at identifying less than well made shells, & rejecting them before putting all that finishing work in.
We make all our own shells in house. From 8" through 32" in stave, steam bent, & segmented constructions, but we don't supply shells, either to other companies or individual self builders. One reason we don't supply others, is that (& this is nothing personal) we don't trust you to finish the drum in a way that celebrates the timber species & construction of the shell, yet it would still carry our name on it.
Think carefully about exactly what you're trying to achieve, especially in terms of sonic character, before going the self build route. If your design is focussed & well researched, then go for it, & good luck on your journey