No special access issues
The Roadblock is clearly obvious on the long straight next to Llyn Gwynant on the A498. Parking is available by the side of the road and a break in the wall gives access to the boulder.
For the Offroad bloc, begin from the Roadside bloc. Walk uphill trending leftwards to the corner of the field. Cross the small brook first, then the fence (carefully) on your right. Follow a vague path uphill keeping the stream on your right hand side and watching right. Soon, the boulder will become apparent next to the stream hidden in the woods.