All hive boxes, no matter what kind of box or who you buy from, need a good roof if placed in the weather.
A good roof shelters the box from the Sun and rain. If a colony gets too hot it can die. If water runs down the side of the box it can sit in any gaps or joins and over time rot the wood.
A well made box will have no gaps and nicely fitting joins but water or moisture can get in to anything over time. Wood can and does shrink and expand and this can cause gaps for moisture to enter.
Be careful when making your own box or buying a cheap one, check for gaps and nicely fitting joins.
Cottage style roof
Simple Tin Roof
Basic Timber Roof painted yellow
Rusty Tin Roof