5 Add Glue tabs

Select Plugins>Glue Tab.
glue tab plugin
http://github.com/rschenk/Sketchup-Glue-Tab-Plugin/

 

Click on boundary edge to add a glue tab.

Click on the tab.

Press "S" key . Scaling grips will appear around the selected tab.

 

Select a scaling grip and move it to scale the tab.

 

Scale tool
http://help.sketchup.com/en/article/94900
Scaling 2D surface or image entities
http://help.sketchup.com/en/article/94902