Populating Error screens?

Hi,

We are working on sybase 2.1 version everything is well and fine with creation of MBO,

Here are the few queries

1) how to populate error screens when there is no data after calling bapi / RFC ?

2)How to design customized UI Elements like button optimization(e.g size of button or color) we are geting default buttons and all other UI elements how can we customize those elements?

Hoping an earlier Response.

Thanks in advance.

Siva Reddy D.