Step 1:
Make a valley-fold over this line, it's just a little above the center line.

Step 6:
The piece below is the one which is folded until step 3. Turn the piece above. Then slide the edge undicated by the upper arrow behind the edge at the arrow below.

Step 5:
Make 4 of these pieces,  one of them only needs to be folded until step 3 (without step 4).

Step 2:
Make a valley-fold over this line.

Step 4:
Make a valley-fold over this line.

Step 3:
Fold the piece above the black line to the backside of the model by making a mountain-fold over this line.

Step 10:
Make a valley-fold over these 2 lines.

Step 8:
Repeat step 6 with the other 2 pieces

Step 9:
Prefold the model over this line.

Step 7:
Here a part of step 6 is already done.

Step 16:
Make a valley-fold over these 4 lines. The 4 pieces on the left, between the black lines, are all of equal size.

Step 15:
This euro note is for the base of the tower. Make a mountain-fold over these 2 lines.

Step 12:
These lines are already prefolded. Now, make a valley-fold to get them in the right direction.

Step 11:
And make a valley-fold over these 2 lines. Then unfold the folds of step 10 and 11

Step 14:
The main part of the tower is done now...

Step 13:
Slide the edges indicated by the arrows on the right behind the edges indicated by the arrows on the left. The two orange lines show the length of the pieces which are slided behind the edges on the left.

Step 21:
And the base of the tower is ready too...

Step 19:
Push the piece below the black line to the inside of the model by making a mountain-fold over this line.

Step 20:
Push the piece below this line to the inside too. Note: This is a diagonal line, we're making the tower of pisa. Make the same fold on the other side of the model, see upper arrow.

Step 18:
Push the flap indicated by the arrow on the right inside the opening at the arrow on the left.

Step 17:
Make a mountain-fold over these 2 black lines.

Step 22:
This note is for the top of the tower. Fold the paper in half over this line.

Step 28:
And the top of the tower is done too...

Step 25:
Hold the model on a table, the same as I do here. Press the inner layer of the edge downwards, see arrow.

Step 26:
Press the inner layer downwards on more places, see arrow as example.

Step 24:
Slide the piece indicated by the arrow below inside the piece at the upper arrow.

Step 23:
Roll the model up by pulling the pieces indicated by the arrows towards each other.

Step 29:
Push the top of the tower in the main-piece, see arrow.

Step 27:
Press the edge of the model flat between two fingers at the places indicated by the 2 arrows. (This is on the place where you've connected the 2 ends in step 24). Now the model can't open by itself anymore.

Step 30:
And push/slide the main-piece in the base of the tower.