These are joined together by strips of thick plastic card, 12mm wide: these join the sections together (refer to diagram below. I obtained drawings from Vicgrain many years ago).
|Concrete vertical under construction. Still to be painted and detailed, plus roof to be fitted.|
http://www2.nmit.vic.edu.au/~david/emrc2/resources/silos/Silo_Geelong_300dpi.gif. Beware, this is a very large file.
The roof was then constructed from plastic card. I used Evergreen Metal siding 4526, as this is close in appearance to corrugated iron.