I don't build too often due to my lack of skills but I do practice art in real life so I can understand the frustrations of not being able to come up with concepts, something I like to do is keep an "inspiration" highlight on my Instagram. I save things to it that ether interest me or get me to think, this can be done with a folder on your computer or anything for that matter. That way you can look back at things you've liked recently or in the past in order to help get some inspiration juices flowing.
I personally like builds where nature is taking over the structure, this might be a bit over down but they are still some of my favorite concepts. I also really enjoy water based builds such as; fishbowl, ocean, lake, river, pond, etc...