more often then not "custom" domes are premade from trial and error. Not to you're motor. Every builder has predetermined specs for certain builds and needs of the customer. Like they have a dome for each size motor they like 95% of the time. Some builders like more or less band width, some recommend smaller cc domes, some like different squish clearance etc....
This doesnt mean they are not good domes. just ask questions. There has been plenty of custom domes "for a motor" sold that detonate or blow motors up.