Instructions
Choose the "Eccentric" trait and the "Born Salesman and Born Saleswoman" trait when creating your Sim. These traits will enable you to move up levels quickly as an inventor, which will allow you to reach the stage where you can build a robot.
Go to the Science Lab in any of the towns and take an inventing class. To take the class, you will need to buy the Scraptronic Workbench, which costs 1,250 Simoleans.
Let your Sim invent and sell the inventions for profit. Eleven career levels exist for inventor, and you will need to reach the 10th level, called "Robotics Dealer." To reach this level, you must generate $88,905 in total profits from your inventions. Leave a skill opportunity slot open for the Simbot.
Collect one palladium, 10 life fruit, 100 scrap and one heart-cut pink diamond to make a Simbot. You can do this by adventuring around the map. Move the Sim to the workbench and select the Simbot from his skill slot. Your Sim will make the robot in his workshop. This will take a little over 12 hours of Sims time. This time can be sped up using the Time control.