For many it’s a famous rose. It’s pretty, easy to fold and anyone should know how to do one. Be it for your sweetheart, for you or just for show it is a lovable rose.
You can find step by step instructions in Oribara Web, in the Rose for Peace project. The Rose for Peace is because this is a Professional High School Project in Fukuyama, a city in the Hiroshima district. Getting the hint? You can get more info about the city in the Fukuyama City site (english). As for the Rose, the page is in japanese but you really have step by step photos and in some “tricky” steps there is a video. All you need to know: yellow line is for valley folds, green line is for mountain folds, blue line identifies the previous creases. Easy? It gets easier; 2 nice buttons take you for the next or the previous step. You have no excuse for not doing a rose!
My advice: the first rose should be done with 15×15 or 20×20 paper. After that you can change sizes and go to 10×10. The smaller I’ve done is 7.5×7.5 and it’s a bit too small. It gets somewhat harder to fold. A 15×15 paper gives you a rose of 4.5×4.5×3.5 (width x length x height).
Edit: all measures in centimetres…