In Onshape, you can use the Loft tool to make a model gradually change shape from one end to the other. For example, a 3D model might be square at the bottom and circular on the top. You can use two or more shapes with the Loft tool and you can also create a path for the shape to follow when it is extruded.
The examples below show a 3D model that changes from a square shape at the bottom to a circular shape at the top, a 3D model that follows a curved path as it changes shape from the bottom to the top, and a 3D model that uses 3D shapes (square at the bottom, rectangle in the middle, and circle at the top.
This tutorial also shows you how to create offset planes which will come in very handy for your drawings.
Watch the video below to learn how to use the Loft tool in Onshape.