It's a pretty easy part, too. You can use everything from heavy velvet to wool or synthetics. Heavy material tends to flow nicer.
1 will either be from your shoulders to the bottom or (if you want a short riding cloak "Type Robin Hood") to the middle of your thighs. That's 180 or 90cm respectively. Be sure to add a few cm when you cut and adjust the final length when everything else is done. 2 is 2m.
Sew a wide hem at the top and pull a string through. Pull the string tight until the cloak fits around your shoulder and then close the openings of the hem with a few stitches. Cut off the string (see to it that it doesn't slip back in). Hold the cloak closed with a brooch or a clasp.
Now try the cloak on and ask a friend to cut it at the bottom. You may want to round the front edges or even fur-line the hem (gray area). If you used very heavy material, let the cloth hang in a closet for some weeks before you cut the rim, it will stretch a few centimeters.
If you want to do a lining inside, be sure to add it before you hem the cloak.
In the end, hem it all around and you might want to add a hood. Don't ask me about how to do that, I never did. Measures are (3) about 40cm x 45cm (4). Sew the two parts together at the red line and sew to the collar of your cloak at the green line.
Try those easy patterns first and when you find the result nice but not good enough, try to adjust it to your needs. Have fun sewing.
Here is another easy-made cloak with big effect.
Cut a rectangle from the fabric, about as high as the distance from your shoulders to your toes and about 2m wide. Fold 45cm on each side to the middle. That will leave an opening of about 20cm at the front. Sew the shoulders. Take a needle with a sturdy string and pull it through the shoulder. draw the string together so the cloak will fall in folds around your shoulders.
To finish, let a friend cut the cloak to it's final length and seam it. You could decorate the hemline with fur or lace, too.
Cloak 3 is a short riding mantle. You cut out the whole "not-quite-semicircle" for the back and the two halves for the front. The width from left to right should be about the width from wrist to wrist when you spread your arms. A little shorter maybe.
Cut out the smallest possible hole at the top to fit around your neck.
The cloak is sewed together at the sides except for two holes for your hands, which are lined with fur.
The neck is also lined with fur and a button disguised beneath it to keep the mantle closed.
When wearing it, the hands are usually kept inside the cloak. This garment keeps you very warm but also allows swift movements.