Hello, I was pretty mad when i went to roll out a clean install of Windows 10 as my boot camp and it fails at the end. But, I worked at it for a few hours and found an answer that i hope works for you. You will need:
Windows 10 ISO file from Microsoft.
16GB blank USB flash disk
You must run all OSX updates in the App Store to make sure your on the latest Bootcamp utility
This is for a fresh Windows 10 install (it will wipe out all your files on any previous boot camp install so back them up)
Part 1 - prepping the disk
1. Run the Boot Camp Utility and let it remove any existing partition if it prompts you. If it doesn't prompt you, just close it, we will open it again later.
2. Run the OSX Disk Utility, Select your hard drive with your OSX install on the left side. (dont click on a partition, but on the drive itself - its usually highest in the list)
3. Click the partition button and you will see your Macintosh HD parition (Dont mess with this one, its all your MAC stuff). Click the + sign at the bottom and it will add a new partition.
4. Click directly on that new partition on the left and give it a name (ie BOOTCAMP) and (important) change the format to ExFAT.
5. Drag the little divider between the two partitions to size the BOOTCAMP partition appropriate to what you want. You DO NOT want to take all the free space from your Mac. 20GB is a minimum for Win10 and it depends on how many apps your going to install. Click APPLY and wait till its done. Note: i try to make the size of the new partition something unique so I can distinguish it from other partitions when installing windows. So for my example, lets say my OSX drive is 500GB and my window partition is going to be 75GB. I will note that for the Windows install part.
Part 2 - prep your install USB
6. Next you are going to prep a USB drive using the Boot Camp Utility. (16GB size or bigger, make sure it has no files on it). Stick the USB in and run the Bootcamp utility.
7. Select "Create a Windows 7 or later version install disk. This should automatically select the second item for you. Deselect the 3rd item "Install Windows"
8. You will need to point it, when prompted to your Windows 10 ISO and your USB drive. Let it run and it will take a while. What its doing is making a USB with both Windows 10 install (multi partition) and creating a folder called Bootcamp which will include drivers and files needed later to run the hardware.
Part 3 - Installing Windows
9. Now, with the USB in, reboot your mac and hold down OPTION. When the boot menu comes up you will see your OSX/Mac partition as well as a Windows (orange) icon and an EFI (orange) icon. You may see more but those are the ones we are interested in. Select the orange Windows drive.
10. Start by running thru each dialog of the WIndows install. When the installer comes to disk selection, find the partition (in GB) that your created earlier. In my example, i actually see 4 partitions. 2 of them are in MB not GB. So i know these are the wrong ones. The partition 1 is approx 100GB, so i know thats my Mac... dont select that. I located my 75GB drive (approx) and i click on Format and let the utility format the drive.
11. Then you can select that newly formatted drive and click Next.
12. From here on it, its a regular install of Windows. The touchpad will work just fine for clicking and moving, but for right clicking and other stuff, we will fix that later after the install is completed.
13. Note... the install, to complete 100% required 2 reboots. YOU HAVE TO REMEMBER to hold OPTION down when it goes to reboot and select your Bootcamp to boot into, otherwise, it will go into your Mac and not complete the install. If you miss it, dont worry, just reboot and hit OPTION and go into it again. Do not remove the USB yet. Mine needed 2 reboots to complete.
Part 4 - Installing boot camp stuff
14. After your running your newly installed Windows 10, you have one last job to do. Install the boot camp stuff. While in windows open your USB and open the folder called BootCamp. Run setup in there and take the defaults.
15. To customize your touchpad to allow you to right click, tap etc... after boot camp drivers are installed, down at the bottom right, click the arrow to review hidden icons, and open up the BootCamp Control panel. On the first tab, this sets which drive it should boot by default. I leave mine on my mac. On the other tabs let you customize the rest of your touchpad.
I hope this helps you because it was driving me nuts!! Enjoy