My shop was built, to my specification, by a friend. Starting point was 8 'x 4' sheets..
10' 9" x 6' 9" external. 19 mm cladding on 50 mm frames with 12 mm ply inner lining.
Roof, 50 x 50 mm bearers on 2' centres with 12mm cladding on both sides, with glass fibre insulation, as used on the walls,
Pitched roof, 8' high at front, 7'6" at rear, to allow room for the belt cover on the RF25 to be opened full, with the head at then top of the column.
After 11 years the felt was replaced by one piece of EPDM rubber, with plastic trims all round. The gutter is on the.back wall, into a water butt for SWMBO gardening activities..
Floor was 3/4 ply on 8" x 2" bearers (spaced to allow the legs of my folding crane to pass under when inserting machines. Corner to corner difference was 1 mm! Door end was 100 mm framing to accommodate the weight of the fire door!
On the walked on area of the floor, are hard plastic mats giving about 1" spacing for insulation, (and for the swarf to fall through. (Needs cleaning about twice a year, if not removed to recover dropped nuts, bolts washers, parts etc! )
Front is against a low patio wall, rear against 6' wooden fence. The end remote from the door abuts a low earth bank, so the bearers are protected on three sides.
Rigid and cosy!
Steel benches came from the scrapyard at work, One, 6' x 2'6" was cut down, together with a shorter one, to 18" wide. The RF25 sits on another 2'6" wide and cut and flitched from 6' for fit between the wall and the warehouse staging that carries the lathe.
Lighting :2 x 5' fluorescents on the ceiling, augmented by two worklights (now with LED lamps ) for the RF25, and another over the big vice on the narrow fitting bench. The lathe has its own 24V 50W Halogen light, on a goose neck, attached to the Cross Slide.
Power supply is via an RCD in the house to a ring main, with 11 metal clad twin sockets. The one feeding the VFD for the lathe is suppressed in case anything were to be fed back into the mains. The RCD has never yet tripped.
Location is East Anglia, UK, so temperate, and low rainfall area.
Heating is by a thermostatically controlled 2 Kw fan heater. Runs for about 10 mins at first then rarely!
Ventilation by a 6" fan set high in the backwall to extract with fixed intake low down on the wall.
In winter, a 60W tubular heater, under the fitting bench, is left switched on. Being small, after a couple of days, the shop feels warmer than outside!
Rust is almost unknown.
Hope that gives some ideas for the new workshop
Howard