I too agree with David & Ash, as this is your first build, stick to the book, get it on the road & then maybe change things to how you,d like them (obviously not the chassis design) but other area,s where you can "put your own mark" on your car,
or
build another, from the knowledge you,ll have gained by building a book spec car then your next project won,t be so daunting.
As for using round tube, just think of all those "fish mouth" joints
try keeping 2 bits of round steel at the correct angle with a welding magnet on them
whatever you decide to embark on , i wish you good luck with your build
cheers
andy