One thing we do have to bear in mind is the catflap. If we had something that closed like a door, it would drive the poor moggies mad trying to get through it
Especially when they come running at top speed from the other end of the garden and dive at it.
BOING!!

ha ha i can just imagine that Rosendula
i put the frame on three small hinges,top middle and bottom to stop warping, then in the frame and the screen i put two small magnets (like the ones that you have on toilet cabinets with the mirrors) so it clicks shut, all the frame is drilled and screwed for strenght then the mesh stapled, when we had the high winds it did'nt budge at all.
The screen just acts like a normal door, just make sure when you put your center strenghthener on the frame that i dose'nt get in the way of the handle of your door then both will open and close fine
If you want to put a cat flap in at the bottom of the screen door make a smaller frame (the same size as the cat flap)and screw it to the screen frame then staple the mesh to the cat flap, once it is secure cut away the mesh so the cat flap opens and you should be ok ...screen door with cat flap..after a short while they will get used to it just like the cat flap in the door.
I hope this helps
all the best
russ

Respect to all, be kind to all and you shall reap what you sow.
old tree man,
aka..... Russ