Only a contractor can provide you that estimate EACH home as it's own character. Depends on what is required, your specifications, permits , size of addition, concrete slab , roof etc etc etc etc.
PS I am a general contractor much more than you can imagine is involved for a room addition.
Lynn911 Dallas Realtor & Consultant, Loan Officer, Credit Repair Advisor
The Michael Group - Dallas Business Journal Top Ranked Realtors