Question 1:
Hi, I would like to program a bot, which if you / msg BOT House writes, building a house! Is that possible?
Question 2:
Where could I program this bot?
First of all, you should learn to program
Which language do you recommend? Java, right?
If you want to program a Minecraft plugin then Java is the right choice if it makes sense to learn Java through Minecraft plugins is another thing. But you can learn how to program.