Ad code writing [on hold]

Ad code writing [on hold]

I have a little problem, so I'm writing to you. I have some websites (only
3), and I want to advertise on a larger site (I buy banner surface).
Since there was only one banner surface funds, but all three want to
advertise my site, so some of the code should show another site that
randomly rotate banners in 3 turns me say, with a weighted 33%.
I figured out a solution to uploading via FTP 3 html files, these files
inserted in the banner (468x60 banners) and this 3 file reference
entertain it in the code, which you can then show the foreign side.
However, I can not write this code because I do not understand it ...
Can you help me with this?
Many thanks!