Creating a Parts list

Hi everyone, I am new to the forum and this is my first question. I am creating a sheet that can figure the parts of a cabinet. The problem is I need to compile a list of the parts from several lists. The columns are Box, Width, Length, # of pieces. These columns are repeated three times for the back bottom and sides. The list needs to combine duplicates and collate from largest to smallest from all three lists. Thanks Thomas

youd have 1 Parts list.
every unique part. no repeats.

then youd have Composite part list. (composed from the Parts list above)
[item], [part], Wd, Len, [Qty]
Table1, 2x4 3ft, 4
Table1, 4x4 1" board, 1
Table1, 1/2" screws, 8

etc..

Hard to say something without sample excel workbook but one way is a PivotTable