Building height data input into dxf format file

[andes]

I used a free software program donwloaded in the internet to convert the coordinate data of several buildings as a dxf format file. But the program doesn't provide a function to input the buliding height data in the dxf file. Because I want to write a program to add this information in the dxf file, I have to know the format of the dxf file. So, anyone can teach me:

1) How can I do to input the building height data in the dxf format?

2) What is the format of the dxf file [ ASCII (text) ] when I add the building height information into it?

Thank you very much!!!