What reason would you have for a top enterence? I realize heat rises and, if we have anything, it's heat in Florida but, is that really necessary.
Reasons for top entrance:
No mice, skunks, possums, or dead bees blocking the entrance.
Slanted roof to also allow rain run off (and work with air circulation).
Mike has his reasons but he lives up north. http://www.bushfarms.com/bees.htm
Probably the biggest headaches that can come of this are either (a) the bees will build bridge comb and solidly attach it to the frames or (b) supering when the honeyflow comes as, bees like to have thier brood nest near the enterence and, store their honey in a verticle fassion.
I didn't say it was perfect(but close). I expected the burr comb. I already have to deal with it between the permacomb frames, but burr comb does not bother me. I kinda like it. Burr comb attached to the roof isn't strong enough to really lock it in place unless you let the box build it up for a couple of months without looking in the hive. I check every other day. It doesn't have time to get strong enough because I keep breaking it.
Where the brood is and the honey is doesn't bother me, I doubt it will bother bees. As bees in the wild can have top, bottom, or middle entrances. If the comb is built on a branch they will have all the entrances they want.
However, this would probably be a great ventilation aid if used, in conjunction, with a standard Bottom board so that they have ventilation and an entrance at both hive extremeties. I debated about trying something like that once but, I decided it'd be easier just to drill holes in the supers.
I think a top and bottom entrance would be fine if that is what you want and your hive is strong. A weak hive would not be able to protect to many entrances. I wanted a screened bottom for better air circulation. Some people also use the screen bottom for mite control. I didn't want to make swiss cheese of my supers.
I thought about this also. Bees tend to make air circulate if the hive gets to hot by fanning the hive by flapping their wings near the entrance. It can cause many bees to work the entrance instead of doing other things, like make honey and encourage the queen to lay eggs. I wanted to try to reduce the amount of bees that had to do that.