TD Matrix

I'm trying to create a term document matrix where the columns are the
documents, the rows are the terms in the documents, and the cells are a
weight of term frequency in the document. My problem is the documents
are all different lengths. So when I add a new document, if the document
length is greater than the max document length in the matrix, I have to
resize the matrix and do a cbind operation. 
 
Does anyone know of an easier way?