This tip from David Edward Gaskill illustrates how to create simple 3D objects in Autodesk Inventor without starting with a sketch plane and a 2D sketch:
Here is a tip for Inventor that allows you to create a box, cylinder, torus, or sphere without having to create any 2D geometry.
Start a new part, then go to the 3D model ribbon (click the image for a larger view).
Select box or use the arrow-down button for more selections.
Sketch to pick the center for the object to be created, and then drag to the desired shape. Once you have sketched the shape, the extrude dialog box will come up. Place the extrude distance. You now have a box without having to create a sketch plane first. This saves several steps, and is fully editable.