The Meaning of Life, the Universe, and Everything.
I'm more of a "Survival Mode" kind of guy, and I don't really build much in Creative Mode besides a roller-coaster here and there. So, if you have any ideas on what I should build in Creative Mode, post them here. I'll include an image of what I built in a reply to the comment that featured the idea.
Say something silly, Laugh 'til it hurts, Take a risk, Sing out loud, Rock the boat, Shake things up, Flirt with disaster, Buy something frivolous, Color outside the lines, Cause a scene, Order dessert, Make waves, Get carried away, Have a great day!
I have the same issues, and I tend to quickly get bored with Creative mode compared to survival. However, lately, I've taken on re-creating locations from real life, and my other favorite games. As Canary suggested above, try re-making your hometown, house, or an IRL location you're familiar with. Otherwise, try building a map from another game you like, such as the square from City 17 in Half-Life 2, de_Dust from Couter Strike, or the Site from SCP: Containment Breach.
If it's an original idea you're looking for, try out redstone contraptions. There's always something someone hasn't made yet, or ways to improve or change existing designs. Try your hand at a 3x3 piston door, an intricate trap, or a Rube-Goldberg machine of some kind.
U think at a pretty small . Try combining ur favourite style with something large , big ! Like ... I very modern building meant for developing high-tech or , I u like the medieval style , try finding a very tall mountain and build a castle on top of it , then if u want to continue , start making a village down the mountain .