For us we thought we were done after 3 kids. I still had the "need" for a girl but was quite happy with my boys. However when the youngest started Prep, I started getting clucky big time and DH agreed we could have "just one more"
4 was a big family and boy or girl this was the last. However he was born and that "girl need" kicked in again and I asked DH if we could try again. Given there was 6 years between number 3 and 4 and I felt S needed a playmate of his own as his brothers were all so much older than him. Plus I really wanted to try and sway for my girl.
If he said really didnt want anymore and was truely against it I would put it out of my head (yeah right ) and get on with being a Mum to four sons. Luckily he said yes though and even luckily still we were blessed with Lady.

For me its not about the space or the finances as to me you work with what you have/havent got.
For me my biggest thing is time, or lack there of.
Whether it be individual time for each kid, Mummy and Daddy time or that illusive time for myself. I always seem to have time for bloody housework or trying to juggle the bills though

I never set out to have five children and if was talking to my 16yr old self now telling her that I would be a mother of 5 one day I can imagine her face but I wouldnt change it for the world and given the choice I would do it again in a heartbeat but for me I am now done. I feel complete.