Thanks for the reply.
At least one nuke defence in the main part of the base makes sense.
We always build them as soon as we have a few T3 energy generators up, because we know at the 35 min mark they will come and we want to have plenty of defence.
So somewhere not too long after reaching T3, but maybe not have them fill up competely since they cost a fair amount of mass to build them.
First I must say that my friends and I really like this AI, well done 
But we think we may have found a small issue.
This was on seton's clutch and happend in two separate games.
We were 1 hour+ into the game and we had to defend against nukes and experimentals from the enemy AI. But when we fired a nuke ourselfs from the backmost spot, the AI had a massive base but no nuke defenses.
We think this is caused by the AI not knowning we had build the nuke launcher (no units could get near the base in the back).
Could you tell us if the AI should always be builiding a nuke defence?