documentation/tutorial.md

@@ -163,6 +163,10 @@ Beams oriented along the **X axis**, used to carry purlins or panels across the
 | `RafterLength` | meters | Length of each rafter |
 | `NumberOfRafters` | — | Number of rafters per group (1–10) |
 
+![Structure types](uploads/structure/Rectangular_Rafter.png)
+
+figure 4 - Show a rafter with a rectangular Raftershape and how parameters RafterWidth, RafterHeight and RafterLength are used to define the dimensions of the rafter.
+
 ###### Diagonals
 
 Diagonal bracing bars connecting two poles to stiffen the structure against lateral loads.