Hi Cedarpro,

This article should help you set up the1:1 scale print job in SketchUp.
Printing to Scale –SketchUp Sage Site

Generally I refrain from comment on others methods outside the focus of this forum, SketchUp 3D modeling.
Nonetheless, the premise of an 18’ long paper pattern compels me to ask if you’ve considered the linear error that may occur in a print job of that length compounded by the inherent dimensional instability of paper.
Perhaps a high degree of dimensional accuracy isn’t all that important to the project at hand, you didn’t say.
Just curious...

-Geo