/usr/include/root/Reflex/Builder/ is in libroot-core-dev 5.34.19+dfsg-1.2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/root/Reflex/Builder/ClassBuilder.h
/usr/include/root/Reflex/Builder/CollectionProxy.h
/usr/include/root/Reflex/Builder/DictSelection.h
/usr/include/root/Reflex/Builder/EnumBuilder.h
/usr/include/root/Reflex/Builder/FunctionBuilder.h
/usr/include/root/Reflex/Builder/GenreflexMemberBuilder.h
/usr/include/root/Reflex/Builder/NamespaceBuilder.h
/usr/include/root/Reflex/Builder/NewDelFunctions.h
/usr/include/root/Reflex/Builder/OnDemandBuilder.h
/usr/include/root/Reflex/Builder/OnDemandBuilderForScope.h
/usr/include/root/Reflex/Builder/ReflexBuilder.h
/usr/include/root/Reflex/Builder/TypeBuilder.h
/usr/include/root/Reflex/Builder/TypedefBuilder.h
/usr/include/root/Reflex/Builder/UnionBuilder.h
/usr/include/root/Reflex/Builder/VariableBuilder.h