I am not sure that your area has companies that sell metal buildings, or the cost differences, however, in America, one can build a Steel Building as a residence for less than 10% of traditional homes.

Crystal ball time sadly. They always talk of housing bubbles and such, truth is, growing population will continue to hold up housing prices. The best trick is to get into the market in a small way. Then more of your repayments come off the principal rather than get lost as interest. Then once you have got the loan down some you can always upgrade. Also, it is great to take in boarders, help with the costs. And yes, like here in Oz, the UK house prices seem very high.
As always, by the worst house in teh best street and improve it, same goes with suburbs and towns.