gobel wrote:
which means that it can not be all done with archistair!
Sure you can do it with archistair. You'll just need to use the custom feature. Just draw a fill for the first step, and then another fill for the regular steps above. Then select them and use them to build the stair.
Actually, you may even be able to modify one of the standard stairs. We've always stayed away from this feature, but it seemed that you could modify the stair from its hotspots once it was placed. Experiment at your leisure.