Do I need to hire temporary stairs for double story build?

I’m owner building a double story house and wondering if we need to hire temporary stairs during the build ... ie to delay the install of the actual staircase to avoid damage.

Or would the tradies just use a ladder to get to the second floor?

I only ask because I paid to have the cost estimated and a temporary stair case was one of the items on the estimate.

I've never heard of such a thing but there's no doubt if the temporary stairs are set in place it's going to save you money.

Ask yourself if you had to quote a job where you'd have to struggle with tools and material onto an upper floor, would you quote more?

Our stairs are going in at towards the end of the build - our builder does it as a matter of course to avoid damage. Currently we've got scaffolding and a ladder set up in the stairwell, which is working fine (no different from external scaffolding in terms of tools and materials). Heavy material loads are simply craned in through an upstairs window (currently without its largest pane for exactly that reason) - a lot easier than carrying up temporary stairs (especially for larger items, e.g. plasterboard).

That being said, though, depending on the price for temporary stairs I might consider it for the ease factor, especially if I were owner-building.

Especially, when one day of crane hire costs you a fortune, not even to mention cost of scaffolding hire.

Mostly we're just using the crane trucks used by our suppliers at no extra charge. We've hired a bigger crane twice, but that was for loads that couldn't go up stairs anyway. If you had to hire a crane specifically then yeah, that'd quickly add up. The scaffolding hire is only a few hundred $ (for us, at least), and we'd need to pay at least some of that anyway to properly finish the stairwell void.

It all comes down to cost-benefit - I'm curious to know how much temporary stairs cost? I admit that most of the builds I've worked with have been single-storey, and only the current one (with us as clients for once) is double-storey. Just guessing off the recent stair quotes I've seem, I'm guessing around $2-3K? In which case it's roughly scaffolding hire plus 2-3 crane sessions (at our prices, anyway). As I said, though, it might be worth it just for the convenience factor anyway (plus as lackey mentioned, might get cheaper quotes as well).

Scaffolding will be needed anyway. With regards to lifting stuff, you are right, if you have a small crane or forklift, then you can generally lift it up via window - you would only need to lift plaster (once) and some joinery (later) anyway.

I wonder why the staircase is late on the build, as generally you get staircase during fixing stage and ideally before plastering starts.

If you've got a feature timber staircase (like us and possibly the OP), then putting it in as late as possible minimises potential damage by following trades. Also, if you're doing fancy precision things around cut stringers then you might also need it to be after plastering and painting anyway so you can get the edging right.

On the other hand, if you're using MDF stairs that'll be finished over (so you're not so worried about surface damage), then it probably makes more sense to install them earlier, so you get the benefits of them during the build.

Ah, I see.
Probably would require staining after as well?

Possibly - I'm not actually sure on that point in our case, but it could be a factor in some situations.