Room size is 16ft, wide 4/12 pitch ridge beam is set at 32ins. Above top plate ht. to top of beam. Heal ht. on existing truss is 4 1/4" above existing top plate. I'm using 2/12,s for rafters. My fascias will match but my heal cut is way tolong approx. 26ins. How do I correct this

Determine first the length of the tail you want 26" or so, place your speed square on the end of the rafter, 'crown edge' and mark a 4/12 pitch using the rafter marks on the square. Cut that. Measure approx. 8' 5" from the toe. From there place your speed square on the rafter and scribe a line down the rafter, just as you did the first time. At 4 1/4" from the top, scribe a line perpendicular, ' back towards the heal of the first cut' to the rafter line you just scribed this will be your C-cut. Add your tail length and your healcut should be just right.

http://www.apexhomeinspections.biz/articles/framing%20guidelines.pdf

Check this out it may help