If you didn't know, you have to draw the symbol in the black box that shows you ...

If you didn't know, you have to draw the symbol in the black box that shows you what shape to draw. I had trouble with furniture building too, but you'll get the hang of it soon enough (took me 2 tries). OK, here are the steps:
1. Quick save before building (in case you screw up)
2. Wait for the small tan box that moves from left to right across the screen to start to drop.(box has the symbol on it)
3. As soon as the small box starts to drop, draw the symbol in the direction indicated.
4. If you drew it succesfully, you should hear a chime. Move on to the next shape.
(Note: the game will only register the symbol you drew when the block begins to drop to the bottom of the screen.)