If you make a chair from wood you bought at home depot with your own drawn plans ... your scratch building
If you make a chair from wood you bought at home depot and a set of purchased, etc plans.. your plans building
If you make a chair from a box of unfinished parts requriing cutting, shaping and glueing to make a structure and assemble youur structures into a chair requiring add' work...your kit building
If you make a chair from a box full of finished ready to assmeble pieces from IKEA your assembling (ARS - Almost ready to sit)
The key is "some 'assembley' required". When you see this on things you know exactly what it means.. a screwdriver and maybe a hammer. No cutting.. no sanding.. no shaping.. no finishing.

Or something like that.

I find myself moving from kits to kit bashing to soon plans building..