Hi, I'm 15 and I love to sing, I'm not very good a writing songs so id be very greatfull if someone would write one for me... please? I want it to be about how...
'i didn't know what I had until it was gone.. '... RnB genre type.

Are you just writing lyrics? Or are you writing the music too?

I want to write both lyrics and music... I know its rude to ask some one else to do it for me.. but I'm really terrible.. evry time I try to write.. my mind goes blank! :( I'm only 15, and don't have any money so I'm hoping if your willing to help it would for free?? Xxx

Well yes.
What type of instrument will you compose the music on? Piano, guitar, etc?

On the piano.. 4/4 - I want it to be really catchy/powerful yet emotional (like... e.g Leona Lewis-Happy), if you could do that? I know in my question I said I wanted it to be about not knowing/realising what I had until it was gone, but I changed my mind, I would like it to be about how " I was always told that I would never achieve my dreams, that I should just give up but then.. I stand up and say that I will be heard, that I will achieve my dreams and become someone. Something like that anyway... whatever you think is good :) thanks x

Well. I can't play piano. Or guitar. So we'll start with lyrics.

From that sentence, it would seem "dreams" is the key word.
So lets try a basic chorus:

And they told me I couldn't achieve my /dreams/
But I knew that's not what it /seems/
I can stand up and will be /someone/
Against the odd I will not be /undone/

Yes, that's a good start, yeah I like it :)
I've always found the opening verse-introduction and bridge difficult to come up with... maybe we could use the word 'bridge' its quite relevant. Something like its 'a long never ending bridge, but ill someday reach the end?? '

Concerning the chorus, change and add your own words though, you don't have to use what I've said, its only an example

Well that line along, could be the bridge, as its powerful enough on its own...

You'll need about 2 verses...
OK so break it down, the first verse can be about doubt and what not, then the 2nd verse could be about overcomming the doubt and succeeding

Thus your telling a story in the song.

The 1st verse could start like a phrase like

"when i was little..."
"For many years of my life..."
"I used to walk an uneven road..."
"I was always looked down on..."
Etc etc

They are more 1st person story telling ideas. You may instead want to try 3rd person:

"She walked an uneven road..."
Etc