How did God come up with the idea of creating humans?

it was an experiment gone bad....

Basically its sort of like when we come up with the idea to have children of our own. We want to watch them and enjoy them and look forward to seeing our own attributes in them. Consider the following along with a bible. There is an online version at www.watchtower.org ;)

The Bible teaches that God created humans for a purpose beyond simply breeding. We were made in God’s “image,” with the capacity to reflect his attributes, especially love, justice, wisdom, and power. Add the unique traits of humans that were mentioned earlier, and it becomes clear why the Bible sets humans above animals. The Bible, in fact, reveals that God created humans with not only the desire to live forever but also the ability to enjoy the fulfillment of that desire in a righteous new world of God’s making.—Genesis 1:27, 28; Psalm 37:9-11, 29; Ecclesiastes 3:11; John 3:16; Revelation 21:3, 4.

Im muslim and believe that GOD decide to Create the human as successor in the earth.

The God Yahweh's scientific knowledge advanced over eras of evolution to learn how to create more and more advanced forms of life.

After humans created him.

There is Absolutely no answer for this. God the Lord Jesus Christ, is full of miracles and beauty anything is possible through him. He came up with humans as a test of love and belief for him. The bible says (in my words) " if you follow and accept Christ and believe in him for all hes done you will go to heaven" and that's all were on earth for is to see if were worthy of going to heaven and being with him.

When he wasn't thinking clearly. Never understood how anyone can say God is perfect when he created such imperfection.

He needed some answers to some questions we do not know, so we where made as an experiment so help find these answers

He wanted to share his love around

He wanted to have company, he wanted people to be with him so he wasn't the only thing ever.

Need something to test his biological weapons on.