The tombs at Mada'in Saleh are similar to those in Petra (which was the Nabataean capital and as such, was the site of around 500 such tombs), but with minor differences mostly having to do with the subject matter of the carved reliefs.
Using iron chisels the masons worked from the top of the sandstone to carve out the elaborate tomb facades. The interior of the tombs were often complicated and sometimes contained upwards of 50 burial places.
Bowerstock, G. W. Roman Arabia. Cambridge, MA: Harvard University Press, 1983.
Hammond, Philip C. The Nabataeans--Their History, Culture and Archaeology. Gothenburg, P. Åström (S. vägen 61), 1973.
Healey, John F. The Nabataean Tomb Inscriptions of Mada'in Salih. Oxford: Oxford University Press, 1993.
Taylor, Jane. Petra and the Lost Kingdom of the Nabataeans. Cambridge, MA: Harvard University Press, 2002.