converting to scale

Even if you do decide to stick with feet and inches then it's best to convert all measurements to the lowest common factor. In your case that would be inches.

It just makes the math easier to do.

So, 6 feet 7 inches becomes 79 inches.

 

Unless you want to find 4.65691 inches on a ruler, you really should go metric. You'd have 414 centimeters which whould scale down to 11.799 cm or 117.99 mm. Rounding up from here to 118 mm will give you a much more accurate measure. If you round up or down, you're going to start having parts that don't fit or create odd angles. Our rulers are not set up for this kind  of work with 64ths, 32nds, 16ths, 8ths, quarter and half inch divisions.

OK , but what about the odd size?  like 13 feet 7 inches?   Do I convert it to inches and then do the math?

Just so you know where that 0.02857... number came from (not pulled out of the air) -- one divided by thirty-five (1/35) equals the 0.02857. That number is good for multiplication. If you are partial to division, divide your measurement by 35. Be sure to mind your units -- 6 feet divided by 35 is 0.1714 feet, covert to inches by multiplying by 12 (2.05 inches).

Multiply the actual size by .0285714. It's better to measure the original using centimeters or milimeters to avoid teh odd fractions of inches and feet you'll come up with.