Hi Simon, welcome to the World of Roloplan!
I myself built Roloplans in a lot of different sizes and of different fabrics. Originally the Roloplan is a kite made of cotton. But I also made ones of ripstop and flag fabric. All of them are good flyers if you have the patience to work out a good bridle. The Gierl Roloplan is also a good flyer (I built these kites only in Ripstop so far). Which one is more stable? I would say, the Roloplan is.
If you want to build a Roloplan out of cotton my advice is to use the "Werner Ahlgrimm" plans. The 200/2 is not an original Steiff size.
The original sizes are 80/2, 90/2, 120/2, 150/2, 180/2, 210/2, 240/2, 270/2, 300/2, 330/2 and 360/2. And of course some of them were available as 180/3 and so on.
I think, the 180/2 is a good one to start with.
Try to find a kind of cotton about 100 to 130gr/squaremeter. And take rods of Ramin or bamboo.
If you are in need of plans let me know. I have some of them on my computer.
I hope you can understand my englisch - I'm a bit out of use. School is over since a long time
