"Build and design from Lego pieces"
BlockCAD is a 3D model design and rendering tool that you will design from Lego pieces, the famous block building game you played with when you were a kid.
This program has more than twenty different types of parts. They are grouped in the lower part of the screen, select a type and you will see the different components: for example windows and all the pieces will be displayed to create windows that you can use in your designs.
Best of all it is a free tool, worst of all it may not be too easy to use as the editor is not too intuitive. But if you have patience and you are a passionate layman surely this application will know how to take advantage.