How to do it? A T bar or a row of tiles through the centre of the ceiling? If you are looking for similar-sized edge tiles on opposite ends, then there are two options.
It is fairly simple to calculate the size of the end (edge) tiles. Example calculation: ceiling length = 13 feet 4 inches (160 inches)
tile size 2 feet (24 inches)
Divide 160 inches by 24 to get the full-sized tiles in this row;
160 ÷ 24 = 6.6667
There are six full-sized tiles in this row.
Subtract the combined length of 6 tiles from the total ceiling length and divide this amount by two to get the size of the edge tile;
160 - (6 * 24) = 160 - 144 = 16 ÷ 2 = 8
The edge tiles will be 8 inches each.
With this layout, a bar runs through the centre of the ceiling.
If you are not happy with the 8-inch edge tile size, you can change this, as there are two options to make opposite tiles the same size. If you use the 24-inch tiles, add one tile's width to the leftover 16 inches and divide this result by two to get the edge tiles size;
16 + 24 = 40 ÷ 2 = 20
Now the edge tiles are 20 inches each.
ceiling length = 13 feet 4 inches (160 inches)
tile size 4 feet (48 inches)
It works the same way using 48-inch tiles. Divide the length of the ceiling by the size of the tile to get the full tile amount;
160 ÷ 48 = 3.33
There are three full tiles in this layout.
Subtract the combined length of 3 tiles from the total ceiling length and divide this amount by two to get the size of the edge tile;
160 - (3 * 48) = 160 - 114 = 16 ÷ 2 = 8
The size of the edge tiles is 8 inches.
For a larger edge tile, add 4 feet to the 16 inches and divide this result by two;
16 + 48 = 64 ÷ 2 = 32
Now the edge tiles area 32 inches each.
A change in the layout can affect the material count of the ceiling! Plan your layout before you do a material count.