Options:

• Framing lumber
  • + Less processing, more environmentally friendly
• Engineered wood
  • - Less environmentally friendly to produce
  • - Need to be careful to avoid moisture damage
  • + Can come from recycled wood
  • + Easier construction
  • + Easier to run wires/pipes through it

Conclusion: Go with engineered wood but make sure the vapour/air barries + ventilation make sense in conjuction with it to avoid moisture damage.

Cost: $18,000 = $10 / sqft (wide range $2-12, assume slightly higher end) * 1800sqft

References:

• Wood frame materials
• Wood frame construction
• Framing cost