In this tutorial I selected the Default preset from the welcome window.

Then opened the 3D World.

Once inside you will see a cube, sun and a camera.

In the assets panel on the left, lets double click the cube so we can set it as a Physics object.

While the start node is selected, lets enable the Physics tick box on the options panel to the right.

Then a whole new set of options will show. You will also see that the Collision Shape for this object is a cube. Which is what we needed. 

In Buildbox 3, some of the object is defaulted to have a cube collision shape. It is always best to check and change if necessary.

To check the collision shape, you need to click the Collision Shape Editor button on the upper right hand side of the scene editor.

From there, you have the ability to move, rotate and/or scale your collision shape.

Let us try to add a new asset and edit its collision shape. To do this, lets click + Asset Library button.

Then select the shape you would like to add and select Add to Library

After adding it to the Library, you will find your selected asset under the category Objects to the right. From here, you can drag and drop your object to any scene that you desire.

Just like what we did with the cube, lets double click the cone and enable the Physics tick box.

After doing that, you will see the Collision Shape is currently set to cube and not a cone.

And when we click the drop down arrow, there is no cone option. In this instance, let us select Mesh.

Then click the edit button for Collision Mesh image.

It will then open the Mesh Manager. Here you can select cone and then save.

Now when you click the Collision Shape Editor, you will see that its collision shape perfectly matches the object shape.