Grass Bug

oh that is caused by having blocks placed too close to the surface under a tall grass area. What you can do is use the F5 "paint" tool and paint the region short green grass that way you avoid the flickering tall grass texture but your area looks like it has been mowed. Else you can place your roof blocks a bit lower below the surface

It's unfortunately a limitation of the way how the current grass occlusion is implemented. As @Minotorious said, this happens when blocks (or construction elements, objects etc) are placed too close beneath the surface...
I think it's about time to get rid of this issue, it will be fixed with the next update