Raised beds plans

I'm just about in a position to start building some raised beds in my garden and would appreciate some advice please.

I read a topic a couple of weeks ago when someone recommended laying raised beds North to South, is this the commonly held view or just one persons opinion? and if this is the best way to lay them can someone explain why as the recommendation for siting a greenhouse is to position it East to West.

Also, due to the area where the beds are going being lower lying than the rest of the garden it flooded during the heavy rains recently. We took some advise and raised the level by adding a couple of inches of limestone chippings (which will hopefully impove drainage). The beds are going to be about 18inches high, will it be ok just putting top soil into the beds on top of the chippings or will this affect the alkalinity of the soil?

Thanks in advance for any advice.

I agree with Green Owl. My beds are N-S oriented as I too have no other choice other than super long beds which I don't want. As for output, mine do just fine with ample hummus added to the soil and regular waterings.