I have never roached a horse but we used to keep our mules' manes trimmed short. We would essentially use a pair of sheep shears (the old manual ones that look sort of like scissors). That's what I used on bridle paths for a long time until I got a pair of electric clippers.
If I planned to roach a horse, I'd just take the electric clippers to them and trim them the same way as I did the bridle path.
Oh, and post-trim pix are a must