There are plenty of ideas for tractors that you can look up and decide about.
For my Silkies I would prefer that they be in a more enclosed little coop with a dirt run that is covered with tin or PVC roofing. They can't stand to be in wind or rain so the more enclosed for them the better but with access to sunlight, fresh air and good grass.
You can look through the coop designs on here or check out a few web sites.
At this point in time mine are going in and out of a coop with a ramp, I close the pop door at night and they have an open top pen to use during the day. My biggest problem was making sure they stayed warm this winter. I had 2 Silkie roos in my Quik pens until about 2 weeks ago. I brought them into the shed for night and now just have them in a open top fence during the day. If the wind blows or there is a chance of rain, I keep them loose in the shed.
If you are asking how big.....ha! It can never be too big! You will be adding more and more before you know it. I suggest that in a tractor 4X6', you could put 3 easily. Maybe 4 if they are really good kids. I am a huge fan of not overcrowding. The more space the better.
