Fermenting is easy. Glass is best to do it in, preferably in something that has a lid, but cling wrap can be put over the top in place of a lid.
You add their food and then water (un-chlorinated) - the water level should be well above the level of the food as the food will absorb some and...
Another option, seeing as you only have 4 birds, is to keep them inside, maybe in your laundry if you have a spare corner. Indoor guinea pig or rabbit cages are great. We have one that is two stories as we have a female that does not like our golden male (she is dark, tibetan coloured) so she...