[Build it] I reduced the size of the object and it became flat.

If the object becomes flat when reduced in size, check the [Align] feature!
The [Align] feature is arranged at regular intervals, allowing the Object to move-rotate-control the size. 

▼ [Align] feature (Left:ON / Right:OFF) mode

When the [Align] feature is ON mode,
1) Objects move at regular intervals.
2) Objects rotate at a certain angle.
3) Objects are resized to a certain size.

If you want to freely resize the object,
Click the [Align] button at the top of your work environment to switch it OFF!