Really old one, where I misunderstood XD ...
(complete maximum length: 68,217,339,393 Bytes - a whopping 63.53 GiB)
ushort tileId
ushort layerDataLength
byte[layerDataLength] layerData (for all Tiles; parsed by Tile)
byte #rows
uint[#rows] bytes offset from start of last one (from start of file for first)