kinda funny the UT ag extension ofice told me muscovies were fine and legal and that it was only illegal in some states LOL.
for housing runners ive been told 2.5 sqft per bird INDOORS is minimum, with more being preferable (4sqft per bird ideally and even more if your prone to realy long bouts of bad weather where theyd be locked inside.
i dont think it realy matters if the house is raised or not but rats will eat the eggs and mice are drawn to duck food so making it in such a way that rodents cant dig in is best bet.
runners are aparently one of the best free ranging ducks because of thier speed, tendency to stay fairly tight in a group and general skittishenss...but they are at risk from the same things chickens are, hawks, racoons ect and any larger predator.
some people offer thier runners nest boxes, some offer something more akin to a nesting platform, and others just put a realy thick layer of straw at one end of the duck house as one big communal nesting area...
runners dont perch (and there terrible flyers, but they can climb if the incentive is right) generally speaking though a 24" fence is tall enough to keep them where you want them and they dont need roosting poles ect so height of the house isnt as important either id say 24-36" tall would give sufficent head room if space was at a premium...
runners unlike other ducks dont NEED a pond (though they do enjoy one), but they are just as messy as any other duck so when planning housing easy clean out is a must.
my personal plan is to set up an area under my soon to be rabbit hutches (which will have a solid floor so no droppings on the ducks lol) the hutch base will be 4x8 so im planning for 6 runners to do a 4x4 enclosed space and a 4x4 roofed wire space and then theyll be able to free range around the garden once its fully fenced. untill then ill be setting up a low fence around their space (about 2ft tall) so i can open their "lock down" area and let them run around the back area close to the house. once the property is fully fenced theyll be allowed to fre range but right now my property isnt realy set up in such a way that it would be safe (the neighbor has a rather jumpy pitty who while is very frightend of people (runs away from people) is a little too interested in other animals, and occasionally they "let him off to run" (yup hes on a chain in the back yard 24/7) so fencing is going to be a must before i free range anything.