digraph bars {

node [shape=plaintext]
a_filename [label="filename1"]
b_filename [label="filename2"]
c_filename [label="for very very long filenames"]

# \r aligns the sizes to the right of the bars.
# don't know if you wanted that but i thought it looked neat.
node [shape=box, style=filled, color=orange]
a_bar [label="size1\r", width=5]
b_bar [label="size2\r", width=3]
c_bar [label="size3\r", width=7]

edge [style=invis]

# align the left sides of the bars. also coincidentally
# aligns the right sides of the filename labels...
a_bar:w->b_bar:w->c_bar:w

# uncomment this if you want left-aligned filenames instead:
#a_filename:e->b_filename:e->c_filename:e

# or this for centered filenames:
#a_filename->b_filename->c_filename

rank=same {a_filename->a_bar}
rank=same {b_filename->b_bar}
rank=same {c_filename->c_bar}

}