Find ExtrudeEdgesByRails [or the whole EEby... tools zipped]. I'd make it in two mirrored halves as it looks symmetrical. Use 'weld.rb' to make part of the outline a single 'curve'. Repeat for the rest of the outline. Now you have two curves that can become 'rails'. Draw a third curve (perhaps a very flat arc) to for a profile. Use EEbyRails picking them as prompted [repeat pick on profile unless you want it to end slightly differently in which case make another curve/melding-profile... It should make a mesh of the surface. Then process it as needed - here's a visual clue... I know it's not the same shape but I did it as quick example for you...[image: ZEud_Untitled.png]

Finally installed the plugins i wanted - ToolsOnsurface - the problem seemed to of been my safari browser which would unzip and rename the the files automatically - some browsers cant handle the spaces in file names so fills them with other characters - so switched to mozilla firefox for the downloads and was able to extract the files in plugins folder myself with no problems

There's a curved stair tutorial here... If you don't have a 2D CAD plan [as used in the example] simply draw the 2D plan in Sketchup first and group it, then work off that... http://forums.sketchucation.com/viewtopic.php?p=158602#p158602