Thanks to everyone, I'm glad you like it.
Yes it is really buggy
and Scorpion, you are right. The code always tries to replace for example 4 tiles of the same type by one bigger tile and that's why some panels become invisible if they are not meant to be placed next to each other (pipes).
For own tiles just replace the tile1.tga (64x64), tile1b.tga (128x64), tile1c.tga (256x64), tile2.tga ... and so one with your tiles and/or modify the code to your wishes. Open the script file for more information.
If I have enough time I will continue to work on this project.
Felix