How to add/save a new page format?

I would like to add a new page format to the list of options in Libre Ofiice Writer. I write books in my spare time and I would like the option to set up a page size, margin spacing, etc. once, save it and have it be selectable from the page format list in the future. Is there a way to do this or do I have to make a document template instead?

Yes, you can create new page style.

When you write books you need e.g. “Left side” and “Right side”. These page style already exist.

Create a new page style:

Right-click e.g. on the page style “Left side” and select “Change …”. In the dialog box “Page style” in the tab “Organise” you can assign a new name, e.g. “My left side”.
In the other tabs you can make your desired settings. Click OK.

Place the cursor on the open page and double-click the page style.

Now you can e.g. save your new “left side” as a template.

Note: “Templates” are files with which a collection of styles can be saved permanently and made easily available for future documents without the styles having to be recreated manually.

@Hrbrgr: vocabulary issue! Update your answer to replace “page template” by “page style”. Mention that “templates” are files used to store permanently a collection of styles and make them easily available for future documents without the need to recreate manually the styles

@ajlittoz, danke. Sehr aufmerksam.

ebot: bitte sehr!

This is not precisely what I am looking for. I was able to create a new style defining my page size and margins. Libre office has a mirrored page option that makes the left and right side margins flipped, perfect for a book. What I really wanted was to add a Paper Format in the Page area of the Page Style editor so I didn’t have to make a custom page size, does this option exist?

The path I have described is effective.