How to create this type of 3d object

[Kaysar Zamy]

 

[Monika Gause · Accepted solution]

You would draw a rounded square.

You would also draw the decorations and make each of them into a symbol.

Then apply the Classic Extrude 3D effect.

And apply the decoration as artwork.

If you don't mind this turning into pixels, use 3D and materials (the new 3D effect)

[Anna Lander]

In addition to Monika's post: if you use 3D And Material, you will get the shadows from the effect. If you use Classic 3D, you will need to create the shadows: draw rounded rectangles  (or copy the original one), fill them gray, transform as needed, apply Blur effect with the desired amount, and set Blending mode as Multiply.