I have only two big tips.
1) Research a lot of jail maps figure out the layouts and how the Ts and CTs would move around, rebel, etc. It's all about the gameplay. I would look into break_final as an excellent example of a map with nothing but is a lot of fun because you can rebel and escape easily. Challenge for both teams.
2) Plan / draw / sketch your map out before you start making it. Nothing is worse than spending 50 hours and finding out your map isn't going to cut it. Look into other maps like i've said, architecture etc, whatever stimulates your mind. Even if your technical skills don't cut it, you can learn on the way.