When thinking of a cover that is able to withstand all the element,s and still be top trumps, canvas covers spring to mind. This is because they have been used for many a years in the past, and have always done their job of keeping out the rain and cold sufficiently. Here is an article on different types of canvas covers that one can use as roof for one’s tree house.
If you know that your tree house is stable, and that you won’t be changing it around any time soon, your safest bet would be to go for the permanent canvas covers. This would be made to fit your tree house, and come in sheets that act as a whole roof. There would be no openings where rain water could get through. The downside to this is that in the summer, when the sun is shining, you won’t be able to remove the roof to let the rays in. This can also be taken as a positive thing, to protect your little ones from the sun. With a permanent roof, you can also furnish your tree house, with peace of mind that none of the furnishings and belongings are going to get damaged or blown away.
As with the permanent covers, retractable covers are made to fit your tree house, and so cannot be moved around once they are set and made stable. But they can allow for opening and closing the roof so to speak, you can close them in the winter to help protect the tree house from the elements, and have them open in the spring when the sun is shining. It is also good to allow sun in when it is needed, say you decided to wash the tree house, having the roof retracted would contribute to it drying quickly.
Having panels is also a good idea, as they can be moved about, and don’t have to be a permanent fixture. You can change them up in position, and in the angle in which they lie, as you wish. Maybe you want them horizontal one day, but would prefer them to be at an angle when it is raining, so that the rain can just run off.
The most versatile option would be to have a tent set up; one that you can assemble and disassemble as you please, come rain or shine. It is the most make shift option, as you can make it suit the needs of the tree house, not the tree house suiting the needs of the canvas cover. It is all about making it work for you.
Having a tree house is a great pleasure. One which everyone should appreciate and not take for granted. It needs to be taken care of. After all, it is battling the elements on a daily basis. It is pointless spending all the time and money to build it, only to let is go to ruins once you have finished it.