If you're viewing this page, you've probably bought my book. Thank you!
My book states the knowledge I had at the time I wrote the book. The number of possibilities with saggar firing is large and it is impossible to want to capture everything.

In my book I recommend making a saggar no bigger than 30 x 30 cm and letting the kiln cool down in a controlled manner. This will prevent the saggar from bursting in most cases.
However, if you still want to work with a larger saggar

Paper saggar
You make a paper saggar with paper and clay slib. You build it up in a form layer by layer.
Brenda McMahon often works with paper saggars.

Aluminum saggar
Aluminum saggars are used regularly, but always in a gas oven. I have no experience with it myself, but you can find (English) websites with information.

Flower pot as a saggar

I didn't get any results with a regular flower pot (top right) as saggar, but with a flower pot with a thicker wall (bottom right) it went well.
The hole is at the bottom, so put it on a triangle so that oxygen can get in. I also let this cool down slowly after the firing.

It can be beautiful (or useful) to glaze a work after the saggar firing. In chapter 5 I write that it is possible to glaze the outside (without terra sigillata) without losing (much) color. However, I had only fired up to 1050 C there. I notice myself, and hear from others, that things do not always go well at higher temperatures.