Hello, I've been having this one problem since i've joined ParkCrafters. Whenever I try to create and save a custom structure in the Building Editor of RCT3, there is always a bunch of missing essential chunks, such as windows and doors. I'm only using base game assets, and I make sure all items are in the save selection radius. Even if I save a larger area, the items are still missing. I had no mods installed when I tried this, and just so you know, I wass using the Complete Edition, I think the same thing happens on the Platinum version too. If anyone is having a similar problem or has a solution, please let me know. Custom base-game items are the only thing i'm capable of making at the moment, and this problem does not help. Sorry I did not mention this earlier, even though i've been having problems with it for so long.

Are you using any terraforming when building the structures? If so, when you save, is brings anything that was raised up with the ground back down to ground level when you reload the file from the saved buildings section.

Adding to what Bookworm said, you might try turning on transparency and seeing if the missing items have been lowered underground. You said you tried making the selection area larger, try making it considerably larger, like 5 tile widths, and try again. Hope one of these ideas will work for you.

All structures where made on flat ground, I only raised items by holding "SHIFT", not only that, even items on ground level are gone, it's the SPECIFIC items that are gone, but i'll check back after testing some things out.

EDIT: Thank you JB, I had to increase the save area, and it saved the whole building.

Edited June 8Jun 8 by Nicole Bertsch
Problem was solved.