Quick answer: An addition should answer a precise need. More square footage is the result; the starting point is what the existing house cannot do for you now.
Name the job the new space must do
A quiet office, first-floor bedroom, larger kitchen, laundry space, or family room each has different adjacency, privacy, storage, and access needs.
Study the connection to the existing house
The new space must meet the old one at the roof, foundation, walls, floors, heating and cooling, electrical, plumbing, and finishes. Ask about each connection.
Related service: Home additions.
Consider the site before the room
Setbacks, grade, drainage, access, utilities, and exterior circulation should be discussed before an interior layout is treated as final.
Build a decision sequence
Separate the questions that require design or authority review from product selections that can wait. Early decisions should reduce later rework.
Before you move forward
Keep the scope, selections, approvals, and any project changes in writing. If a claim about availability, licensing, insurance, price, timing, or warranty matters to your decision, request it directly and retain the documentation.