Steel was used as framing for housing quite commonly after the last war when the speed of erection was important to solve the housing shortage. It fell out of favour about 40 years ago mainly because you have to use expensive lifting equipment. It has, however, made a comeback recently. The cost of the two materials are similar but using a steel frame would mean bringing in a specialist subcontractor and this would increase the cost. It would be surprising if you were able to make any significant savings by using steel instead of timber.