Been talking about this a lot in chat, and I'm sure everyone there is more-or-less sick of hearing about it by now. Figured it was time to post some pics.
Getting started (the linoleum didn't work out), but shows the space formerly occupied by my off-the-shelf plastic tent I had been using to keep Neps and other things.
Didn't bother getting pics of the framing, so this is next in line. Basically just built a box with 4x4's in the corners, plus two interior rafters. Almost everything is held together with brackets, since there was no maneuvering room to screw the boards together on the outside.
And the interior, with the mylar hung, the floor (which is a 10'x25' roll of 6 mil plastic folded over several times and stapled to the baseboards) covered in rubber mulch to protect the plastic from getting torn and provide more surface area for the evaporation of any spilled or leaked water.
Now I need to start building tables, and get the misting system and heater in place. Ventilation can probably wait a little while, but eventually I'll be installing a fan for that as well.