I am planning to have a building constructed near an oasis in a sandy desert (it's a mausoleum or sepulcher, but very large - about the size of the average home). And it'll be about 100-200 feet away from the oasis, preferably on an elevation. I need to know about building near an oasis and desert/dune building in general. Most importantly: the foundation, materials, avoiding hazards like the water table, resisting erosion, etc. This is a medieval era, so we can use building materials and techniques from the high Middle Ages but no later.