Garage Construction: This can range from $50 to $150 per square foot, depending on the complexity of the design and finishes. Let's use a mid-range estimate of $100 per square foot.
$100/sq ft * 40 ft * 30 ft = $120,000

Garage Doors: Garage doors can range from $500 to several thousand dollars each, depending on the type and quality.
3 doors * $1,000 (average cost per door) = $3,000

Interior Stairs: The cost of interior stairs can vary. A rough estimate might be around $1,000 to $5,000.

Upstairs Game Room: This will depend on the level of finishes. A mid-range estimate might be $50,000 to $75,000.

Buck Stove: $1,000 to $2,000.

Please note that these are rough estimates, and actual costs can vary. It's advisable to consult with local contractors to get more accurate quotes based on your specific requirements and local construction costs.