It would be nice to know how many ducklings you would have to house beforehand- but a little hard if you are letting mum sit. I have a few different brooders that I can use in different weather conditions and number of ducklings.
At the moment my youngest - from two weeks old down to one day olds - are in my lounge room. The older are in a very large cardboard box with newspaper and pine shavings on the bottom. The 3 that have just hatched are in a plaastic recycling tub bought from Bunnings. The light I use is just a small clip on lamp bought at the same place.
Outside I have a wire rabbit cage that will house about 5 ducklings up to 3 weeks old. I have a pen in the back shed made with colour bond fencing pannels on a wood frame for bad weather or cold nights.
I also made a brooder pen... but I will have to go search for the photos- It was fairly easy to make, and finished in a day.
And last- A huge wooden crate I brought home from work. Very solid- I have just made a mesh lid for it.
I will go have a look for some pics for you........