Jamieson, Fausset and Brown on Isaiah 22:16

16. What ... whom--The prophet accosts Shebna at the very place where he was building a grand sepulcher for himself and his family (compare Is 14:18; Ge 23:1-20; 49:29; 50:13). "What (business) hast thou here, and whom hast thou (of thy family, who is likely to be buried) here, that thou buildest," &c., seeing that thou art soon to be deposed from office and carried into captivity? [Maurer].

on high--Sepulchres were made in the highest rocks (2Ch 32:33, Margin).

habitation for himself--compare "his own house" (Is 14:18).