In Windows, SketchUp prints to a printer, not to a format. If you object to the extra clicks when you print, then create a duplicate printer that prints to landscape instead of portrait.

1. Open the printers and faxes folder and right click on your printer, in this example 'HP100'. Select Properties.
2. Click on Ports tab, look for the port, something like "USB001" "Virtual printer port..." . Write it down.
3. Start the Add Printer wizard, and on the port drop down select the exact same port above.
4. On the driver page, select the printer (if displayed) or put in the printer's driver disk.
5. At the 'replace or use the installed driver' prompt, use the installed one.
   -- It is your call whether to make this 'new' printer your default printer.
6. In the printer's folder, rename the printer to something like 'HP100 landscape' or 'SketchUps printer'
7. Right click on the printer, select Printing Preferences.
8. Make Landscape the Printer Orientation, click on Apply then on the OK button. Just clicking the 'OK' button doesn't always change it permanently.