When setting up a VM, no matter what OS I select, I am unable to select the size and thus unable to create a VM. What did I miss?
Can you let me know which steps you are going through? I choose a "Windows Server" through the marketplace in the Azure Portal and am able to both select the VM size and create the VM.
I had this same issue, but for me it seemed to be due to the region I had selected for the VM. I was originally trying to create it in UK South, but when I changed to Europe West, it allowed me to select a VM size.
Hope this helps.