Help & troubleshooting for channels on your Roku device, including adding/removing channels, logging in to, authenticating, or activating a channel, channel-specific playback issues, assistance contacting channel publishers to report issues, and adjusting channel-specific settings.
Your best option is to discuss with several local antenna contractors.
Also, use Google earth website to see if you have line of sight to a transmitter (70 miles..curvature of earth and terrain may make reception impossible). Plot the line on google earth and "fly it" to see if it has a chance.
Likely to be a significant cost and a big chunk of metal on a big pole.