Hi Nicola
I have been working here in Spain as a self emloyed builder for 6 years now. The first 4 and half years were okay, but after that it has become more difficult to earn a living.
Most of the windows here are alluminum plastic is rarely used. We live inland, however the work situation could be different nearer the coast.
The social security for self employed is 252€ per month. You have to pay this even if you haven't any work, which can be difficult especially for us as we have a family.
On saying this there are other benifits of living here.