Researching a PhD project.....manipulating plants to produce antibodies!

I thinking of doing my PhD in manipulating plants to produce antibodies for humans. Im kinda stuck on the part of working out the the gene that makes the antibody?...i know they are companies online that can produce an specfic antibody from injected a mammal with an antigen. it think i can get 20uL for a cost. i assume i derive the dna sequence from this, thus allowing me to create a the gene.....right?..through an automated technique. i guess my question is...what technique i need to determine the DNA of the antibody?.....how much antibody do i need to use with this technique?...any other advice you could give me would greatly appreciated. Also, understand i havent started the Phd...I am just preparing the research proposal.
Thanks in advance