tl;dr: A remote worker in Portland built an 8'x10' backyard office for $19,478 by using a Tuff Shed as the shell and hiring separate contractors for concrete, electrical (60 amps, permitted), drywall/flooring, and a Daikin mini-split HVAC. Key lessons: upgrade to larger windows than Tuff Shed offers, get multiple quotes (electrician quotes varied 2x), prefer small one-person contractors, run hardwired ethernet, and plan for ventilation (a CO2 monitor revealed the sealed space needs an ERV/HRV). Hiring a full-service ADU builder would have cost $40–50k.