A sapling shelter can be easily built provided you are in an area where woodland is still young. (If there are no suitable saplings available you can make a shelter like this by driving pliable branches into the ground).
You will need to find an area with at least 4 to 6 saplings growing at least an arms length apart. Clear the ground between the saplings, bend the saplings and lash their tops together. Use additional branches to interweave a latticework between the saplings leaving an opening for the door. You can also lay a "ridge-pole" across the top, as in a tent.
Consolidate the structure with ferns and turf. The sapling leaves and additional foliage will provide a natural covering for the hut. Of course If you have access to some form of waterproof sheeting you can drape it over the saplings. Either stake or weight down the edges with stones or logs. ( If you are going to have a small fire inside of the shelter, have an opening at the top for smoke to escape).