Instructions
Select the "Clone" icon in the menu at the bottom of the design window; it is the icon second from the left.
Click on the brick that you wish to replicate.
Move the cloned brick to the position you want by either using the mouse or the arrow keys on your keyboard.
Repeat this process on any brick that you wish to replicate.
Change the color or material of the brick by clicking on the "Paint" icon; this is the third icon from the right in the menu at the bottom of the screen.
Click on the brick you wish to change and choose what color or material you wish to apply and the brick will change accordingly.