Match the base
Set the dome diameter to the outside width of the supporting wall. A hollow dome uses less material and leaves usable interior space; a filled dome is normally useful only for small decorative forms.
Read layers from the base upward
The layer selector begins at the widest usable ring. Complete each ring, verify its center against the building axes, then move one block upward. Temporary columns through the center make alignment easier.
Handle short top layers
Near the crown, block counts fall quickly. Do not smooth the roof by eye: follow the plan until the final cap is placed. Afterwards, add trim or a second material without changing the structural outline.