In this instructable I will teach you how to make a "piggie bank" only out of legos, for this demonstration I will be using the tinkercad website. Disclaimer: I could not get the brick mode to work on tinkercad, but the normal mode should do fine.
Step 1: Base
The first step you are going to do for this creation is to get/find any Lego platform. This can be any width or length, just make sure you have enough legos to accommodate for the base's perimeter and the walls, which should be about 7-8 bricks high. Following that, outline your base's perimeter with bricks. This will help you get a general idea of your layout.
Step 2: Walls
When making your walls you need to account for durability. If you were to make four separate walls for your bank then would most likely fall apart every time it is dropped. That's why overlapping your bricks (as shown) is so necessary. It may seem a little tedious, but it will make all the difference.
Step 3: Final Product
After building up the walls to the level you desire, you'll need to consider what top to put on, if any. Leaving it open will give easy access, but if you are looking to keep your money safe and hidden you could consider building a cover out of the another platform. Personally it was a great use of extra legos and blends in seamlessly with my other legos. Have fun and enjoy!