Looks good! Ventilation is important. You have windows, but won’t always be able to use them if they provide a draft or breeze on the roosts in cold weather. Perhaps upper wall ventilation or livestock fan to pull out the air. Also can have roof vents.
we sometimes get pretty cold here. We have heat, but it doesn’t turn on unless it gets below 15F (programmable). I figure it's not really heating the coop up, it’s taking the bitter edge off. The coop is well Ventilated, so even with the heat it is only a bit warmer than outside. This year temps were mild, then dropped to -10F, quickly, so I was glad we had the heat in there since they hadn’t really gotten acclimated to winter by then. Since you have an electrician handy, add the heat, maybe a programmable Thermostat. The one I have has a plug forheat and a plug for cooling (can connect to a ventilation fan), with programmable upper and lower limits for each. These units are sold many places (got mine on Amazon) and are popular with home brewers and mushroom growers.
if they are already adding electric, add a plug for future outdoor electric fence if you think you’ll need it and a plug for water in the winter - you’ll need something to keep it from freezing. We also added an outdoor rated timer to add light in fall/winter on a schedule, but that’s personal preference.
good luck
