Here is a simple step by step guide to making 1:5 scale scratch build dreadnaughts. SG dreads are towering 16mm tall from toe to exhaust (over 2 epic infantry tall), while a 40k dread (or the AOBR plastic at any rate) is around 550mm tall (under 2 40k inf tall) this is an attempt to make more accurately sized dread. Finished dreads come out about 11-12mm tall, so pretty much 1:5 scale.  The same method can be used to make Mark IV dreads, Mark IV chaos dreads, iron clad dreads, venerable dreads, chaplain dreads and probably a throne of judgment.
Per dread You will need the following:
about a postage stamp sized area of 1mm plasticard in total
2.5mm of 2mm plastic tube (+2.5mm per power fist, +3mm if Mk IV/chaos/venerable/chaplain)
A selection of thin plastic rod (i use 1mm, 0.8mm and 0.6mm)
4mm thick, 3.5mm tall standard GW sprue
The ability to cut out rectangles is also pivotal...
Stages:
1) Feet – (make these first as off cuts are needed later). Cut some 4mm square bits of 1mm thick plastic. Cut a 1mm square from each corner (keep the bits). Slice the edge of each of the toes thus formed into a slight angle
2)Armour (a) cut a 5mm length of sprue.  Cut out two 4 x 2mm rectangles and two 2.5 x 2mm of 1mm plastic, cutting a 1mm square from one corner of each larger rectangle. Stick the smaller rectangle  at 90° onto the back of the larger, on the end without a square cut out (b). These are the front and top armour plates, stick them onto the sprue ©, with the smaller rectangle on the thinnest (top) face of the sprue and leaving a 2-2.5mm gap between the two plates (d).
3) Sarcophagus- cut two 5mm x 2mm rectangles of 1mm thick plastic, glue on top of each other. When dry cut a very steep angle at one of the thin ends and a shallow angle at  the other. Stick this onto the side of the sprue between the armour plates from the last stage , with the steep cut end on a level with the thin (top) of the spue, the bottom of the sarcophagus should protrude about 1mm past the bottom of the sprue.
4) Exhaust – cut a 3 x 2mm rectangle of 1mm plastic , stick two 1 x 2mm rectangles on top with a 1mm gap and cut an angle along the long edge these small rectangles. Stick this block onto the back of the sprue (eg opposite side from sarcophagus), decorate top with two small slices of rod for exhaust pipes)
5) Hips & decoration– stick two 4 x 2mm rectangles of 1mm plastic together, cut an angle down the ends to form a trapezium. Stick this to the underside of the sprue. Using the 4 1mm squares cut from the feet, cut one into a small trapezium and stick it to the back of the hip block (centred) . Stick one square centred to the front and one underneath, pop the fourth between the armour plates on the top of the torso. Stick some small blocks of 1mm plastic onto the sides of the sprue as well, the arms will stick onto these.
6) legs – cut two 5 x 1.5 mm rectangles of 1mm plastic. Round one end off. File/cut a small incision about 1mm down from the rounded end. Stick a Small slice of rod on one side.
Leg armour – cut two 2.5mm length of 2mm tube. Make a pair of angled cuts into the side of the tube at the top. Slice the tube down in half, giving you two curves shin plates. Stick the shin plates on the front of the leg rectangles, stick a foot on the bottom of the leg. Stick the legs onto the hip block.
7) Arms – so many variants, but the main block of a normal shoulder is just two 3 x 4 mm rectangles of 1mm plastic stuck together with one corner cut off at an angle. Then proceed to attach bits of rod till guns appear! (for a power fist thing use 2mm tube).
Where'd I put me plasticard?
