My oh built ours and they are secure with weatherproof roofs-dunno what cats you have but wouldn't underestimate their ability and determination to "escape" or other cats/dogs ability to get in
If your willing to spend and have a run/runs built-you may as well get secure ones for your peace of mind and their safety
We also have some rubbish weather(in case you'd not noticed
) and without a roof it's not gonna be great for your cat/s on a windy/rainy day