The dome itself a series of self supporting circular brick chains that curve inward until they meet at the keystone at the oven top.
Tiling a pizza oven dome.
You can also frame and decorate the front portion of the dome arch with granite or other materials.
To get a perfect shape dome put the sand in the shape of a dome.
Reading through your replies to various comments it looks like glass or porcelain tiles are best to use and to use a thinset mortar to bond and grout the tiles.
Given the variety of colors and styles of tiles available at hardware stores the design possibilities are huge.
Construction of an igloo dome does not necessarily require a frame if completed by a competent brick layer.
It is to do with the sand and afterward place the bricks onto them.
These ceramic and glass tiles present a very convenient medium to finish the dome of the oven since their flexibility allows them to repeat the shape of the dome.
A brick pizza oven dome is usually constructed as either an igloo or barrel dome out of medium density fire bricks both shapes are constructed in much the same fashion with bricks mortar and usually with a supporting frame.
Then apply a tile and grout sealer to seal the grout.