Decide between a fixed model or a
parametric
model. Build the fixed model from elements and save as an object. This is simple, enough since whatyouseeiswhatyouget.
Search Archicad Help for "Object Saving."
Other: Search the internet for "Object Making with Archicad."
Parametric objects are created line-by-line with GDL code, a variant of the BASIC language that underlines all Archicad. Using code allows for reconfiguring object parameters. For instance, the ability to change sub-element materials or change the number of shelves in a bookshelf. See "GDL Reference Guide" in Archicad help, but this unfriendly document does not teach GDL coding if you don't already understand code. To LEARN GDL, our colleague Nicholson-Cole wrote "The GDL Cookbook."
GDL Cookbook
If you are making objects for yourself, simple models are fine but if you hope to produce professional work, code is the only answer because it isolates parameters.
You can begin a professional object using a model, but this makes dirty code with many lines of extraneous [for the object] code. It takes a while to mine the actual form data from location data.
Good Luck.
Dwight Atkinson