HELP creating geometric shape for 3D printer

[curious aardvark]

is that two pyramids - base to base, attached to another base to base pyramid ?

basically two of these, stuck together along one of the faces ?

double pyramid.jpg

Also dimensions are determined by the slicer before you print. You can make them anything you like :-)
Size of a model like this within a cad program is largely irrelevant.

More pictures wouild be useful - not entirely sure of the shape.
Is this close ?

Untitled.jpg

dp2.jpg