Hmm, when signing in at
https://owner.roku.com/Developer it just returns me to that same page, which doesn't contain a download link.
Through some trial and error I did manage to find the link after all:
http://wwwimg.roku.com/static/sdk/RokuSDK.zip and it does indeed contain the mockup .pptx PowerPoint file. Also good to know that there is a PSD file at
http://wwwimg.roku.com/static/sdk/RokuS ... mplate.zip.
Unfortunately neither has been updated for a long time (2011/2012) and both are missing some screen types, such as the grid screen. Any chance that there are more recent files available anywhere?