We had the attic converted to a room about 4 years ago, to bedroom standards if we ever need to sell.
Velux windows, laminate floor, radiator, fire door, loads of storage space, under the eaves. Our friendly local handyman, Mark Webber built the baseboards in two days, for the price of a couple of medium sized locos, as I had bought the baseboard material (9mm marine ply) and had it cut to size by the builders before the attic was finished (too big to come up the twisty narrow staircase once finished).
The tops of the baseboards are 39 inches off the floor (ideal height for me to work at, and allowed four existing bookcases to slot underneath.) The 2x1 frames are only attached to the room by screws into the skirting board.
The main baseboards are 15ft6 x 11ft6, with a large hole in the middle, and a 3ft x 2ft bit in the corner by the door.

I have a reasonably large collection of mainly RTR 00 stuff from pre grouping to late 1990s sector liveried diesels, and wanted a fairly bland generic canvas to run them on in terms of location. The time period is broadly current, suggesting "heritage" status, though four continuous ovals rather contradicts that. I tend to run one era/ region for a few months then pack it all away and move on. I rarely mix wildly conflicting eras/ regions, except if testing new stock.
As I mainly want to "lineside" through trains, and find much of the DCC sound unappealing, DC is fine, powered these days, by a Gaugemaster Q.

The four photos below date from almost exactly four years ago, just after the boards were built.

I plan to bring this up to date quite quickly.