There is a free preview of 8.1 available to download and try right now but the retail version will of course cost actual money.
I would recommend using W7 to build the PC and install the preview to see what you think of W8.1
There is a learning curve (quite a steep one in switching to W8 as it does a lot of things differently to W7. By which I mean the UI (User interface is different)
As an example I am using it now and then and trying to transition yet simple things like opening and closing an Email are overly complicated and not readily obvious.
Don't get 8.1 Preview now. It will be released retail next month, and you'll just have to reinstall again.
Yes but its free to try now. Why not try it before you buy it ?
Well, if you want to go through the hassle of a full reinstall so soon after....
Trying a 'Preview' is what secondary machines or partitions are for. I have 8.1 on another partition on a secondary laptop. I would not use it on my primary machine.
I like 8.1. I'll be upgrading my primary box, already running Win8 Pro, after it comes out.
many thanks for all the posts. I am running Windows 8.1 to deploy to hundereds of tablets at work so i'm pretty familiar with Win8. I think i'll try Win8 on a seperate partition and see how my games work.