In my mind when I see Roland I see him as Liam Neeson. He's the right build and with the gruff voice and the worldly look he would be perfect.
Josh Holloway could do it.
Tom Hardy could be a good choice.
I don't know if anybody has suggested this before or not, but how about Josh Brolin to play Roland?
I don't think he's tall enough. Roland is at least 6'2". But I suppose they could use some of the tricks from Lord of the Rings to make him look taller...