Hi there.  Wow not easy to find specific information on this one.  There is lots of information out there, but I could not find a specific recommendation for the Willamette Valley. I decided to go on the Portland Rose Society web page and see what they had to say.  Their general recommendation was late February to early March.  They did not differentiate between types of roses but rather by the number of rose bushes you had. Those with lots of rose bushes they recommended starting earlier so that you could be done in time.  Those with only a few bushes could wait a bit.  I did find a University of Illinois publication that provided a bit more information on how.  You may want to visit both places.  Basically, if you prune too early the new growth that the pruning stimulates could be damaged by late frosts, those plants that are damaged by a late frost would then need to be pruned a second time.   Here is the link to the University of Illinois article.  https://extension.illinois.edu/roses/prune.cfm  If you have any more specific rose questions you may want to browse the Portland Rose Society’s website. http://www.portlandrosesociety.org/links.html