Building a cat run

Am contemplating bringing my cats out to be with me when I am in Spain. They are house cats and would not be let roam. So I need to have a solid external cat run constructed, to give them some (albeit Restricted) access to the great outdoors. If such a run could include interesting elements (eg wooden steps, climbing frames etc ) so much the better. Will approach local builders and carpenters but asking if anyone may have recommendations on this type of thing ... Thoughts and suggestions much appreciated.