Bonus room above garage

Hello I have a bonus room connected to my bedroom that is above the garage. It has electric but no insulation so it gets hot like an attic in the summer and cold in winter. I’m just looking for some ideas preferably cheap in easy to make it into a nice little man cave. I would hate to just use such a nice size room for just storage. I will try to include some pics. Thanks.

P.s. I’m a little handy but I don’t want to mess with electric