We move into our house in 11 days, and I sort of think that apart from the obvious up-front expenses like foundation and actual house, it depends on how much of a work in progress you want it to be.

If the builder specialises in sloped blocks then you'd think they'd be prepared for yours, but definitely find out. Often finance is dependent on the soil test and land being surveyed anyway, in case the cost blows out beyond what you can afford.

As for the other things - it just depends on how you want to start out. For us, we compromised on the things that we can sort out later.
- Like we didn't include an alfresco area, because we're handy (okay, well our family are) and we can do it ourselves when we have some spare time and money.
- We have vinyl floors because they're gentler than tiles on little boys sliding around in socks and if we get sick of them in 10 years then they're relatively easy to replace.
- We got our curtains from IKEA because one day I want plantation shutters which I will have to sell a child to buy and I can't decide which child to sell yet.
- We will take awhile to put in a permanent clothesline because I don't know what area gets the most sun. And the same with the garden, I need to know where the sun and wind hits to know what will survive where.
- We have heating, but I imagine air-con will come when we decide we just can't do without it anymore. And when we can afford it.

But yeah, things can be upgraded. When you want better taps, showerhead, oven, curtains, letterbox, driveway, light fixtures, paint colours, benchtop, carpet - that is all stuff you can compromise on for now if you need because it's not incredibly costly to replace down the track.
When you're building you want things like room size and window placement and any garage and storage issues and kitchen and bathroom layout to be right, because they're the things that will cost a packet to change later. If I had a budget, I'd rather spend that money on a house with great kitchen and lots of storage cupboards, and then get the air con later.

So that's my essay for you. It really is great to build, because you can have things just where you want them. You just need to go into it knowing how much everything will cost, and having some things you can compromise on if you need. If it's going to be your forever home, then you might be okay with it being a work in progress - as long as you give yourselves a timeline for things so your backyards still isn't all mud after years of living there!