You have two options:

• Install them in multi boot
• Install windows in a virtual machine

The first one If you install windows later is not recommended, you can have problems if you install Ubuntu after Windows, so you can backup image as (here)[https://askubuntu.com/questions/19901/how-to-make-a-disk-image-and-restore-from-it-later]. Then first install windows and restore ubuntu from the disk image.

But as you said that you want to make Windows your main OS, then it will not be good option to virtualize using second option.

You have two options:

• Install them in multi boot
• Install windows in a virtual machine

The first one If you install windows later is not recommended, you can have problems if you install Ubuntu after Windows, so you can backup image as here. Then first install windows and restore ubuntu from the disk image.

But as you said that you want to make Windows your main OS, then it will not be good option to virtualize using second option.