I don't think the Roku box supports VLC's http streaming - you'll have to use HLS via the new livehttp VLC module. I think you'll have to install a nightly build to get it.
The last time I messed with it my params looked like this:
--sout '#transcode{vcodec=x264,venc=x264,width=624,height=352,fps=23.97,acodec=aac,ab=128,channels=2,samplerate=48000,threads=3}:standard{access=livehttp{seglen=10,delsegs=true,numsegs=10,index=/var/www/mystream.m3u8,index-url=http://machinename/mystream-########.ts},mux=ts,dst=/var/www/mystream-########.ts}}'