If your good with design then why copy.? You'll be bettter designing something that suits your exact needs and is within your skill/equipment range. For instance I've built several machines that size which use profile or steel but no point giving you the designs for them because you can't machine parts and you can't weld.
So to me you either have to design machine so it can be built within your means or Employ someone to help who has the equipment and skills.

Washout is correct regards cost of steel Vs Profile, it's much cheaper. It's the hidden cost's of profile that catch people out, things like T-nuts,Corner brackets Etc and if you try to skimp and not use these then profile is a bitch to work with. It doesn't drill nice, it doesn't Tap nice and you can bet your last £ you'll want to put a hole where there's no material.

Steel on the other hand is much cheaper Per meter if bought from a decent steel stockist, typicly £30-40 per 7.5mtr length of 50x50x3 compared to £25 per/meter(£187.50 per 7.5mtr.!!) of 45x90 profile.
Steel is easy to work with just a few tools, Grinder,Hacksaw, drill and cheap Arc welder. Holes are easy drilled and tapped plus if/when you cock up it's an easy fix to fill hole with weld, grind back and try again.

Look around forum and then design to suit your needs post it up here and we'll point you to any changes that need making.

Word of caution regards electronics is don't buy Cheap drives or Kit packages you see on Ebay etc. It's false economy and leads to head banging problems. Also don't buy them untill needed for warranty reasons and this will probably be several months after frame is started.!