Starting the ball rolling with as basic a structure as possible and the tools I think are required to achieve satisfactory results.
This one is for plasticard and the tools needed.
Start with a reasonable size cutting mat, absolute minimum A4, preferably A3 if youre serious.
A sheet of plasticard, anywhere from 0.60mm up to 1.00mm.
Two steel rules. These are used together, one to give the cutting guide, the other to measure out.
A VERY sharp knife - I use Swann Morton scalpels & qute frequently change blades.
Liquid polly glue.
Then paints & brushes as required to get the finish you want.
That is all that's required - not much.
However before you can start you need a plan. The easiest structure is a 6 x 8 garden shed, there are millions, found everywhere !!
I always make to drawings I've done. Not as hard as it sounds, particularly with the following shed.
Sides 8 feet long, in 4 mm scale that's 32 mm, height flexible, but I used 24 mm. One side has windows so cut out an opening of 20 mm x 6 mm cut 12 mm from the base edge - keep central that is 6 mm from the two ends.
Ends 6 feet wide, in 4 mm that's 24 mm wide, 30 mm to a central ridge line coming down to 24 mm at the edges to match the sides. One end having a doorway cut out 23 mm high & 12 mm wide - Cut clean & save the cutout as that is you door.
Two roof panels 34 mm x 15 mm
Cut some scraps to edge the door frame 2 - 3 mm wide and stick on overlapping into the door space by 1 mm or thereabouts.
Assemble the square on a flat surface making certain all parts are vertical & making as perfect a square as you can ( markings on cutting mats help this)
Attach roof with equal overlap all around the edge.
Cut scraps of plastic abt 1.5 mm wide to make inner door frame, one at top & bottom with one in centre, then two diagonal strips starting hinge side top,
running to latch location on the central door stiffener.
Add 3 window dividers as fine as you can make, for window glazing strips. Stick some clear plastic on the inside to glaze the windows.
Add two hinges & a latch from shreds of scrap plastic.
I finished the roof with a thin strip of paper glued over the ridge.
Then paint as required.

Geoff T.