Any tips on making them looks nice
made this one http://www.openstreetmap.org/?lat=55.8666989207268&lon=12.323049902916&zoom=17 can’t get it perfect round whit Potlatch
In Potlatch: Select the roundabout and press “T”.
One thing that helps is zooming in as far as possible and adding more line segments. It looks like the circle has been improved since the last rendering, so the image currently shown does not match the more detailed drawing that was last uploaded. The rendering should update at some future time.
Looks so much better 
thanks for the help
you’re welcome
Wow. I didn’t know Potlatch could tidy circles, just lines.
If it’s split into multiple segments, I believe you’ll have to use JOSM; select the nodes and hit O.
If it’s split into segments, you can still do it in Potlatch: Create a new way, and let it be a closed way containing all points of the roundabout. Tidy your new road, then delete it again.