I wrote in the German GDL Forum about this topic some years ago.
There are shown different ways.
www.archiforum.info/
If you do not understand any word written there, I can translate the preferred version.
All sample objects (And other) are
download.b-prisma.de/objekte.zip
A demo of my latest favorite version is
www.b-prisma.de/publisher/htmls/satteldach_demo.html
(you need web control installed).
Since ArchiCAD 10 there are new ways to make page turning.
But I haven't tested them until now.
Jochen Suehlo . AC12-27 . MAC OSX 14.4 . WIN11
GDL object creation:
b-prisma.de