Hi Lady Lib,
What you need what you really realy need is a wall bracket with a large extended arm which is strong enough to hold old Rudolph and the sleigh. You then drill a couple of holes preferably into the gable end of your property at a height which is comfortable enough for you to reach from a ladder. You then fasten the sleigh on to the overhang part of the bracket so that Rudolph's feet just touch the roof. Then fasten the bracket to the gable which presumably has holes in it which line up with the drilled holes in the gable.You might need to buy an ariel pole and fasten a piece of aluminum to that which extends over the roof area.
If the above is a no no try lashing the decoration to the chimney.I don't know if you have life insurance but get some before going up a ladder and doing any roof work.Make a will as well and it would be a good idea to get someone to hold the ladder.
Safest bet is to place Rudolph on the front door step and throw brown balls of putty, which look like reindeer droppings,on to the roof .That will save you from having an accident up there.
I once saw a guy slide all the way off a pitched roof which was frosty , luckily when he landed he only suffered a dislocation.
Don't attempt any of this after an egg nog.
If it's not to early Merry Christmas and have a wonderful time and may God bless us one and all.
Edmond.