SQL 2012 :: Length Of Columns In A Table?

I am working on a migration project and need to derive the total length of the columns for a particular table. I have the following query designed for the same:

select
t.name,
sum(c.max_length)
from sys.all_columns c
join sys.all_objects t
on t.object_id = c.object_id
where t.name='test_1'
group by t.name
;

This query gives me correct results except for data types varchar(max), nvarchar and xml for which the max_length is stored as -1 which causes my results to be incorrect when summed up. Is there any other way to find out the maximum data length for such type of columns?

Here is my table DDL:

CREATE TABLE [dbo].[TEST_1](
[COL_1] [bigint] NULL,
[COL_2] [bit] NULL,
[COL_3] [char](10) NULL,
[COL_4] [date] NULL,

[code]....