You need to measure the existing door frame, and select either two 1" by 2" strips that are slightly more than 1½" shorter than the door frame length. You may prefer to use 2" by 2" strips that would be stronger, but we can't guarantee that the same size hinges will support the weight. Ours are 1" by 2" as that was what we had available at the time.
In reality, the strips are ¾" depth by 1½" width, and that affects the other measurements I will be giving you, as you need to "measure twice, and cut once", according to the resources you have available where you live.
Next you need to measure the width of the area you want the door to cover, and you need two strips to run top and bottom of the frame. Our measurement is 26" across the top and bottom. The strips are screwed together. 
Then, in the photo you can see another strip put on end within the frame, to give it support. Based upon figures we have used so far, our measurement for that cross strip support would be 24½", which can be screwed, and/or glued into place as they are not weight bearing.
The wire mesh that is stapled to the frame is ½" square aluminum mesh. This has been strong enough for any cat to climb safely.
For the first temporary door, we used a hook and eye type of attachment, (see left), but Legolas knew how to open these, so we could not take the risk.- This type of door bolt was attached at both ⅛ and ⅝ the way up the door frame. The two bolts are needed to prevent the cat from being able to pry the door using the one bolt as a fulcrum, thereby making enough room to squeeze through.
At right is a view of the other side of the door, showing how the latch fits into the assembly. This is the lower lock.
At left is the upper assembly near the door handle, showing how the lower bolt is attached. The block of wood is a spacer making room for our hands to lift the bolt. The spacer also ensures that there are no wide gaps between the screen door and the door frame that can be manipulated by the cat involved.
The hinge is positioned at normal door height for Steel Butt Hinges, at about ¼ of the way from the floor, and from the top door frame.
