hello,
i had an idea for a customized indicator using the bid and ask volumes.
i wonder if it has been done?
and whether it would give any pert information?

it would simply take the difference of the bid and ask over a user-specified number of bars.
so for example, on a one minute chart, i might have a running tally of the last 10 bars' net bid-ask volume.

the purpose would be to show accumulation or distribution on a specific time frame.

yes, i use the bid/ask histogram now that shows the bid and ask volume for each period.

It's alright, kinda makes it look like an oscillator of sorts. Some of my first bid/ask indicators were simple SMA's of the bid - ask volume... which is equivalent to what you are describing only scaled by a factor (if I understood your post, anyway). In 2008 there are pictures of it on my website. Like... for instance... Daytrading Exxon Mobil Corporation (NYSE: XOM)|Move the Markets but there are lots more if you dig around.

I can't say it's better or worse than the simple bar-by-bar bid-ask volume, because it always depends on what you are wanting to see. Both have their uses.