By floating shelves, you mean ledges affixed to walls? If so, not a great idea...If you're a beginner, you probably have misjudged how wide those shelves have to be--back branches can't touch the wall. Additionally, such shelving means that one side of the tree will remain shaded, which will weaken branching. Rotating the tree every couple of days can help, but that leaves the heat issue--A wall in the summer will both reflect heat onto the trees/containers, as well as act as a "heat sink" which remains hot after the sun goes down. That means the trees immediately next to it will not cool down during the night. This is a critical part of trees' ability to complete photosynthesis, as well as growth. If the containers on the shelves are very small they are more likely to heat up quickly and with that heat, more likely to have root damage from it...Air circulation could also be affected, shelves below could also be shaded out by shelves above...