You would want to use the roScreen/roBitmap/roRegion/roSprite and roTextureManager components to create a custom user interface. It probably will take quite a while. Only one channel has done a clone of the homescreen in Brighscript, which is the DailyBurn channel. I'm not sure its worth your time if you just want to create a Roku channel, except for the learning experience, which would probably be a good one.
- Joel