Surcharges in custom fields for invoice e-mail template

Hi all, 

I am trying to make an e-mail template in Spanish that includes several custom fields. What I want is: 

- field 1: rent 

- field 2: surcharges such as breakfast, additional beds etc. Can be more than one field 

- field 3: VAT/sales tax

- field 4: total of 1+2+3

The problem is field 2: how can i show these surcharges. Also they should be included in field 4 total

Best regards