locate a suitable place for wind turbines could be tricky, you need additional criteria right? like place with high speed and direction of wind,
but if you only use those two criterias (slope and road radius) then this would really simple task
you can use simple method like overlay
for slope, make classification for slope, higher score for flat terrain and small score for rugged terrain
for road, you need a line data and make buffer 100 m and beyond 100 m, highest score for distance beyond 100m
overlay both of data, the combination of beyond 100 distance of road and flat terrain will create highest score, that the place you are looking for