I miss kdrama dvds but then again with all those dvds means less room, why don't they put kdramas on itunes to download legaly, I like to support my favorite kdramas and have it on my pc or tablet to watch anywhere when i have no internet connection.

I been a kdrama addict fan since 2014 since i been watching more and more older dramas. I wanted to get rooftop prince to own but I can't :( 

You mean the legal ones with English sub? Yeah, I don't think they're readily available these days, what with the (legal) streaming sites. I think the popular dramas are available in DVDs, but maybe not with English subs, and you need to get them imported from Korea--so, pricey.
YesAsia is the only place I know of.  I've purchased music CDs from them in the past, but never anything else.

Looking at just the first page for Korean TV Series (Dramas), it seems they have some fairly recent titles (with English subs), but those prices are outrageous:

http://www.yesasia.com/global/en/korea-tv-series-d...

EDIT: Here's Rooftop Prince (with English subs), but it's "temporarily out of stock": 

http://www.yesasia.com/global/rooftop-prince-dvd-1...

well if its temp out of stock then guess it is impossible to get it atm :( 
Rooftop Prince is available on Ebay. I usually use ebay to buy all of my asian drama DVDs, I think they have the most. The only thing that you have to do is check that they explicitly say that there are Good English subtitles, or Excellent English subtitles. 
I once bought a DVD set from Hanbooks, since I couldn't find it anywhere else.  I had a good experience buying from them (I'm in the US, and Hanbooks is also based in the US).  Don't know about international shipping though.

List here:
http://www.hanbooks.com/kotvseonreor.html

And it looks like they have Rooftop Prince in stock too, if you don't mind paying $150 for it:
http://www.hanbooks.com/roprsbstvdrr.html