Motion is a 3D space application, not a 3D modeling application. But if you need to give a 2D layer object depth and thickness, there are two ways to achieve this effect easily. Either use an Extrude filter or create a Replicator. Replication uses more system power, but allows for circling around the object freely. Extrusion uses less system power but has limited rotation view ability. Each technique has its own visual quality, also. Let's look briefly at creating one of each in an educational experiment you can easily follow along with.
I will start with an empty project, be sure the playhead is at the start of the timeline. Hit 'R' for the rectangle tool draw one in the center of the Canvas, hit escape to get out of edit mode, and center it in the Canvas. F4 to the Shape properties and make the fill a light blue. Turn on the Outline block and set Brush Color to a dark blue, set Width to 1. This outline will make the fake sides of our shape a different color than the face.
Finally, use Command-D to duplicate the Rectangle layer, and turn off visibility for the 'copy' layer. Right-click the Group layer and enable the 3D Group option.
To finish our setup off, go to the Object menu select New Camera. F1 for Properties and set Rotation X to -25, Y to +75. Keyframe the Y parameter by clicking the keyframe diamond to make it yellow. Move the playhead to the end of the timeline and keyframe it to 20. Move the playhead back to the start of the Timeline.
With the original Rectangle layer selected (not 'Rectangle Copy'), in the Object menu select Replicate, or hit 'L'. In the Replicator properties, check the 3D option to enable it. Then set Shape to Line, and all Start and End points to 0, except the End Point Z which you should set to -100. Now simply increase the Points until you reach a number of layers that fill the space nicely. In our example try various numbers between 40 and 90.
Notice that you may get a moire pattern using this technique sometimes. This will depend on the object you are working with. Now play the timeline to see how we can spin around it nicely. Set the playhead back to the start of our timeline before continuing.
Be aware also that you can work with multilayered PSD files or with multiple object layers, moving the layers apart on the Z axis, an giving each its own replication thickness for a wonderful 3D effect.
Turn off the Replicator layer's visibility, and turn on the Rectangle Copy layer's visibility. With the Rectangle Copy layer selected, Command-2 for the Library. Go to Filters, to the Stylize collection, and apply the Extrude filter. F3 to the Filters inspector.
A good starting point in this experiment would be keyframing Angle to 25 and Distance to 250. Now set Clipping to 0, Back Size to 0.9, but don't keyframe them. This will give you a nice basic look.
The two parameters to play with now are the Front and Back Brightness. Try out setting the Front to 0.5 and the Back to 0 as a starting point. This gives us some shading.
Now playback the timeline and you can see how this is a drastically different effect from the replication technique, a purely 2 dimensional effect.
To finish up place the playhead at the end of the timeine. Keyframe Angle to 40 and Distance to 100. Now play the timeline and notice how it looks better. You may need to add a Distance keyframe of about 125 at the timeline's halfway point, as the extrude effect may tend to elongate way too much.
With the extrusion technique you cannot achieve 360 degree views, this filter simply will not keyframe in that manner. The replication technique will absolutely allow 360 degree rotation views. Extrude will not require as much rendering for playback. The Replicator will require more horsepower to playback. I hope this gives you some additional tools to create amazing graphics and effects with Motion.