not familiar with the weather of the area but all i can say is if you have very hard frosts in an area( observe before building) then it would be best to build them off contour so cold air can flow. im assuming you get good rainfall so building dead contour is not much of a need, slowing the water down should be more than enough. if the area you are building is dry and a warm spot i would build on contour. of course this is all location dependent. we have mild frosts and light snows but extremely dry summers. so i still build on contour for the need to catch and hold water when things dry up everywhere else.
The ultimate goal of farming is not the growing of crops, but the cultivation and perfection of human beings. - Masanobu Fukuoka
I had 2 unprotected tomatoe plants trellised up, each at the end of a raised bed (about 14 inches tall), They didn't show any signs of frost damage untill it got down below 30 degrees F. The second frost at 25 degrees F exploded the base of the stems with big hunks of ice. Before that they survived several nights of frost around 34 degrees F without any signs of damage, keeping them alive for probably 3 weeks after I noticed everyone else ripping theirs out. I need to figure out a good way to ripen the tomatoes out after they are harvested, because nothing seems to ripen up at these low temperatures.
But I'm getting off topic... The raised beds are on a slight slope and I imagine the 14 inch height is enough to keep the beds above the flow of extra cold air. The beds themselves are 4ft x 6ft rectangles with 4ft spacings between.
Companion Planting Guide by World Permaculture Association