Is it allowed to create an Irc chatroom where you could market, I mean to have your own IRC market chanel?

Sure I guess, but who is going to join it? Besides, there's already a channel for marketing. /join #Market

Just make sure you read the rules which, iirc, is in the topic. (Haven't been in the channel in a while). Just don't spam what you're selling and don't annoy anyone with highlights.

If anyone looking at this is a regular in #market, correct me if I'm wrong.

I just want to add a market chanel at my further forum shop, to make marketing easier and faster and avoid spam(repetately posts like "thank you").

To register an IRC channel: /msg chanserv REGISTER #channelname password description.