Updated 12/20/2003
Roof Spreadsheet
It is often difficult to determine the dimensions needed for a multi-paneled roof, such as what I needed for the scratchbuilt water tower shown on the right.

I have developed a spreadsheet that determines the dimensions of each panel by entering only a couple numbers.
How to Use the Spreadsheet
Click on the spreadsheet image below to open up the spreadsheet and enter your values.  Or, download the spreadsheet to use later by clicking here.  Enter values in the blue fields, only.

First, enter the number of roof panels you want for the roof.  For example, the water tower shown above needed six panels.

Next, enter the angle, in degrees, that you want as the rise or pitch of the roof.  In the example, I wanted the roof to rise 15 degrees.

Then, enter the radius of the structure.  You will need to measure the diameter and divide it by two before you enter it in this field.  The water tower in the example has a diameter of nine feet.  One half of the diameter, or four feet, six inches was entered as the radius.

Finally, enter how much the roof will overhang the structure.  In this case, I wanted the roof to overhang the water tank walls by nine inches.
The spreadsheet will calculate values in the "Results" section that correspond to the image to the right.
Cut a strip of cardboard or styrene the width equal to the value of Y.  Then, along one edge, measure one half of the value of the dimension X.  This value is shown in the results section and is also shown in the drawing below.  Then, measure the full value of the X dimension from that point forward.  Also measure the value of the X dimension along the other edge as shown below.  Make as many panels as you entered in the spreadsheet.  Discard the triangle shown in red.

Glue the panels together along the edge labeled "Z" in the image.  And, you are done!