SQL Margin Calculation gives divide by zero errors

I have a table showing Revenue (R), Cost (C) & Margin (M) values by Product Category for each period 01 > 12 like in the attached
I have substituted the NULL values with 0 using CASE WHEN SUM(C03) IS NULL THEN 0 ELSE SUM(C03) END

In each period margin calc I use CASE to avoid the Divide by Zero errors when the Revenue values are 0 like
CAST (CASE WHEN Sum([R01])= 0 OR Sum([R01]) IS NULL OR Sum([C01]) = 0 OR Sum([C01]) IS NULL THEN 0 ELSE
((Sum([R01]) - Sum([C01]))/(Sum([R01])))*100 END AS DECIMAL(10,2)) AS 'M01',


However I cannot see how is best to create the margin values using the totals.

What I need is ((RTotal-CTotal)/RTotal)*100 where some of the divisor values are 0

Driving me crazy, thanks.

Period		R01  C01  M01%  R02  C02  M02%  R03  C03  M03%  R04  C04  M04% .......   R12  C12  M12%   RTotal  CTotal  MTotal%
Product A   	50   20   60    100  20    80   100    0   100   0    0    0               0    0    0      250    40     ???????

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Example.txt