By chance can u tell me where to find the steel armor? Can it be purchased? Till now I have not paid close attention to armor
Yeah, the Steel can be bought, or made by you at a forge, or looted from certain individuals, but you can buy it/make it before you'll start seeing it on enemies. The Steel Plate won't start coming widely available for awhile, and it still won't be around a lot. The way I got it was if you go into the inn at Whiterun, there's a companion you can get named Uthgerd (I think I spelled it right), she's wearing the steel plate armor. If you beat her in a fist fight, she'll agree to be your follower. You can take her somewhere and kill her and get the steel plate to yourself. The horned steel and iron helmets are pretty common in dungeons.
The armor that will really look dark and nice for a deathknight will be much later levels when you can get ebony and daedric. Daedric shouldn't start dropping until around 46 or so.
Edit: Here's my dual wield guy in the steel plate and horned steel helmet. It's not extremely death knight, but it's about as good as it gets until ebony starts dropping.
[img]http://i4.photobucket.com/albums/y114/aharun/TESV2011-11-1305-28-42-83.jpg[/img]
[img]http://i4.photobucket.com/albums/y114/aharun/TESV2011-11-1304-13-45-82.jpg[/img]