(from Comments of Wrap Pants entry)
I have also added a simpler pattern to the wrap pants under the post "Another Wrap Pants".
For bigger waistline, add from the middle outwards, i.e. red markings. A good guide would be to take the measurements from your current pair of wrap pants. 73cm is half of the waistline of my current pair which is 146cm. Therefore, if the waistline of your current pair is 180cm, then extend 73cm to 90cm.
As for length, just extend the length of the pants legs, as indicated in blue. If you ended up overestimating the length, you can just hem it higher.
You should also try lengthening the 'waistband' piece, i.e. instead of 27cm, try 35cm or even 40cm. You could always just fold them over, if it's too much.
Have fun and would love to see how it turn out.
Cheers, Pegs ;)