This is the BIG misconception. Builders dont have time or are not making enough money on it to build it exact to your setup and needs. All "builders" have "off the shelf" builds 95% of the time. Pre ported, domes pre cut. etc....
Call one of them and ask to get real porting and or real domes for your setup and ask what it will do. If they know what they are doing they can explain the difference and it will cost alot more. The problem is everybody wants it cheapest compared to fastest.
Imo if you want a serious dm call Mat Shearer. He is doing stuff on another level. The best costs.