So true, I needed a second unit (A/C and furnace) installed in the addition I built to the main house for an additional 900 sq. ft. to what I have currently, duct work underneath and all (I live on a ridge). I put together the package unit for the main house myself 30+ years ago - don't believe in split units.

Called one of the big names in town, and he came out saying he needed to measure this and that, along with the specifications how I built it. Telling me I need to install a 60 amp circuit, where to install the intake and vents, etc. Ran the fella off. Then called a local outfit and told them exactly what I wanted and where. Done deal. Nice Carrier package unit for less than $5,000, duct work and all.