MOST ducks do not roost, the exception being Muscovy(which is my main duck breed) and most either make a nest in the bedding and/or will use a nest box... i don't actually have "true" dedicated nest boxes for my ducks and they have not only managed to lay just fine but brooded quite a few nests.
A kiddy poll is absolutely fine or if you wanted to spend more you can buy troughs meant for larger livestock.. i run to two 50GAL troughs and 1 kiddy pool plus another 40GAL trough for my calls lol
One of the main things is the water mess, ducks adore water like chickens like to dig? which means mud, which chickens are not generally particularly found of, that is one of the main differences which makes them trickier roommates.
Plus worth a mention ducks must have water with food and do need access to water that is deep enough to clean nares a simple livestock rubber bowl can suffice. Chickens be mindful they don't drown, i have heard of stories of chickens getting into water levels that are unsafe.
Personally, my standards free range and therefore end up around my ducks.. they basically ignore one another.. my chickens usually don't stay long around the ducks area due to them splashing water. As well the other posters mention of a drake(male duck) mating a hen is a real take note, some have no issues.. i don't but my drakes have ducks of their own and were never actually "raised" with the chickens, they house separate and they have only crossed paths, so don't consider them part of the flock.
So in saying all that i'd stick to ducks ie; girls to keep things a bit less risky. Your chicken choices, we have the silkies they usually flop(dogpile), not much in the way of roosting either, other than a small one a couple inches off the ground. Ours are banties not sure if yours are standard or bantie that you are considering but always keep extreme sizing differences in mind.
Ducks(girls) can usually navigate things fairly well, my Muscovy girls are often checking out my chicken coop.. much to the massive dismay of my hens lol so that means they do climb a ramp to do so but still ducks generally are more agile in water not on land so be mindful of that for building, also ducks don't 'come home to roost' like chickens do, and often require some encouragement to go in at night.
In poor weather times mine often are in but summer? ha they are out chasing night crawlers while the chickens have long gone in.
Any ideas on breeds? i'd get at least two so they have someone whom is their own kind to communicate with. We have some great info in the stickies at the top of the board on brooding ducklings and many threads on breeds. Here, i have buff orpingtons, calls and Muscovy... so bantam, medium and large breed ducks.
