I don't think there's been any confirmation that spell customisation will be included in Skyrim. There was a comment in an interview a while back that they were experimenting with it but weren't sure if it would make it into the final game. PC Gamer UK had a mention of being shown some of Bethesda's experiments along these lines, with a shield spell combined with a lightning spell to give a shield that shocked anything that attacked the player character. They mentioned that at that stage the graphics and animations involved were clearly placeholders.
Given that Bethesda have gone to a lot of effort to polish the graphical variety and complexity of the spells, I wouldn't be surprised if spell creation is very limited in Skyrim, if it's possible at all.
Still, fingers crossed, eh?
I'd say that everything we've seen so far strongly indicates that spellmaking is out, which is something I'm personally okay with. I strongly believe that spellmaking in prior titles was a huge liability that really only gave the player great freedom to utterly destroy any illusion of balance that might have existed, and very much prefer the new method of treating spells as basically equipment in and of themselves. This grants them specific roles and makes balancing them much easier, allowing for a greater degree of polish and also allowing individual effects to have more flexibility. It's perfectly understandable that some people are upset about the loss of customization but in my eyes it makes for more intense and fun casting and it's an acceptable sacrifice.
And PC Gamer UK is the culprit, I see. They said that Circle of Protection was a forcefield that pushed away enemies, and could be combined with Chain Lightning to shock those enemies it pushed away. This was a filthy lie. Circle of Protection seems to be a spell that replaces either Fear or Turn Undead, as it makes enemies run away rather than pushing them.