Condition Zero is different from Counter-Strike in the terms that the development team re-made the original CS maps with new textures, models, etc. They also included the original CS maps, without this remaking.
The result is that CZ comes with a plethora of maps.
Included are maps such as cz_cs_office, cz_de_dust, etc. which are the Condition Zero remakes of the original levels. Also included are maps such as cs_de_stadium and cz_de_vostok which are entirely new Condition Zero levels, and the original CS maps are included for those who want to use the new CZ models and such.
Gameplay/editing/FGD shtuff is all the same, just make sure to use the latest 1.6 FGD. Afaik, there is no deleted scenes FGD available.
Dunno why you'd want to pay someone to make some custom maps.