Hi JMW
it is very easy to get to Roquetas from Almeria by public transport, we have done it loads of times now, if you go outside the airport terminal where people pick up their hire cars/taxis etc there is a bus shelter, the bus runs quite often about every 15 mins I think, this bus you buy the ticket on the bus, the fare last year was 1.80 euro it drops you off in Almeria by the shops, you the walk to the bus station, only a couple of minutes away, and you buy your ticket inside the bus terminal not on the bus, it was 3.60euro I think last year, ask at the desk which bus and they will write it on the top of your ticket (they do it all the time) and you go outside and wait for your bus, they run I think every half an hour, it takes you straight to Roquetas about 30-40 minutes if you want any more info just ask! we are going again this year! we love it there
you can check all the bus times on the Alsa bus website.

Thanks for your help and advice!