You question makes mention of "float" but you later make the point that you made "no mention of water or any other liquid". That certainly creates confusion.
If you are talking about a self-supporting (aka rigid) dome, that is "the nature of the beast" when it comes to Buckminster Fuller domes. However, I need to point out that those are usually "thick-skinned" domes (or dual-domed truss frameworks). Many designs of this type exist and have been conceived, analyzed and built by architectural/engineering firms world-wide. No mystery to those in the know.
If you are referring to a non-rigid dome, namely sheets of polygons (or other patterns) bound together (bonded, glued or stitched) in the appropriate pattern, then inflated, you are simply referring to an inflatable dome, and there is no requirement for that to be a bucky-styled dome; only that it be properly anchored to the foundation and sufficient compressed air volume pumped into the dome to ensure "positive-pressure", which would create a net force greater than the weight of the membrane, thereby supporting the membrane and keeping it from collapsing. Again, many designs of this type exist and have been conceived, analyzed and built by architectural/engineering firms world-wide. No mystery here, either, to those in the know.
If, on the other hand, you did intent to have a dome floating on a lake (or the ocean), you need to ensure that either of the two above design concepts are implemented on a sufficiently inflated base such that the majority of the dome is above the surface of the water. Otherwise, if it is fully submerged, then the flotation must be enough to provide "neutral boyancy" such that the dome is neither surface-piercing, nor so heavy as to sink to the bottom. (On second-thought, surface-piercing might be he most stable configuration.) In this configuration, the "ballast" weight must be below the domed structure and be such that there would be no tendency for the dome to "right" itself (a.k.a. flip upside-down). Without detailed analysis, I could not say whether such a design would be possible. If you did pursue this type of structure, my personal recommendation is to approach (or engage) a naval architect who would be most knowledgeable in the design of maritime vessel buoyancy/stability applicable to this kind of design.