I worked out there for a good few years.
everything A.Plasterer says is right , its not easy and you have numerous hurdles to overcome.
Nice lifestyle though if you make it work , in my case i did lots of jobs and plastering was a nice one for extra dosh when you got it.
Takes a while to get used to the heat but not as bad as you would think , depending on the wind direction.
Work is pretty much the same and pays well if you live in Spain and work for sterling in Gib ( well was in the peseta glory days)
Personality goes a long way , loads of work i got was from making mates in the local bars and letting everyone know i was a plasterer.
There were a few construction companies when i was there but forget the names , they would be in Biancas with the work logo gear on , seemed a bit grim to me , more labouring doing roadworks and stuff.
Wouldnt put you off but you wont be landing there and on the tools just like that , but likewise i turned up with about 50 quid and a pregnant girlfriend and we ended up with a great life with our daughter there.
Its not impossible , good luck