The basic procedure.
Whether it's one sash or a whole set you do them in one batch, which may mean a lot of components, hundreds even, so your cutting list has to be efficient. Handy to have it on a black/white board on the wall so you can see it from wherever you are, and cross reference with whatever pieces of wood are in front of you as the job goes on.
1 Do design drawings for the thing, based on dimensions taken from window openings, room size, whatever it is
2 Draw up a rod i.e. the final working drawing, transferred to a board, usually just cross sections, though an arch etc might need a rod of the elevation on a sheet of ply
Edit. The very first things you mark on the rods are the heights and widths of the opening the thing is going in to. You then work everything from those marks, so they have to be right
3 Work out a cutting list from the rod.
4 Order glass cut, to sizes from the rod, or large sheets to cut it yourself, which I usually do.
5 Cut up sawn stock, according to the cutting list, working from largest sizes/sections/lengths downwards - cut from the smallest pieces of stock available. This is basic stock control and is least wasteful. If you do short pieces too soon you may find you haven't enough long pieces left when you get around to them
All glazing bars treated as through, to be separated later as necessary. You could do all sash boxes as one batch and sashes themselves as another, as long as you are working them from the same rod, but it's handy to get all the planing to size done for everything, in one long session
6 Plane up the sawn components individually, marking all with face and edge marks.
n.b You don’t plane “stock” first, you cut it to size first, with due allowances for planing, and then plane.
7 Start the marking up procedure by stacking components on the rod with edge marks opposite so that you get left/right pieces. Mark one side. This is just a routine even if they aren’t handed - just in case. Stack just a convenient height for marking with a set square. Tick them off the cutting list as you go.
8 Carry marks all round with a pencil.
Mark along the lengths with marking gauges and mortice gauge.
Mark for everything. On a door you can mark up for hinges and hardware. On a sash you can mark for pulleys and pockets etc. You have to decide where these things are going so you might as well mark them on the rod too, rather than thinking of them later.
9 Cut all mortices with bevels for wedges, and tenon cheeks and haunches only - not shoulders yet. Everything is still in the square at this point so rebates and mouldings easy to run. It's handy to work to the lines you've marked up as soon as possible, as they are going to be lost as the work progresses
10 Cut all rebates and mouldings
Going out now - more later!