Our piggies often meet in the middle of the ramp and whereas Buttons & Cornelius are fine and just squeeze past each other it could get a little nasty with Pewter & Benito. So with boys I‘d definitely try to put 2 ramps in 
Plus make sure the ramps have at least sides - if you can make them more tunnel like that would be even better! It‘s less scary for them like that. We let our piggies run through the tunnels that are now their ramps before we put them up so it already smelled like pig and it worked perfectly for our lot! Except for Benito who took some time to realise that he can also walk down the ramp - he just walked upstairs and was stuck because he didn’t understand at first 
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That is really helpful thank you, I was going to make the ramps out of C&C grids with some kind of base so they can grip, they were in a hutch before i got them so they know how to use a ramp (I know some piggies don't like them), I do love that tunnel you made I think my boys would love it too as there tunnel fans lol.It‘s not a c&c but here’s the loft we put on our Midwest. We used to have the exact same loft on our C&C cage but had to take it caused unnecessary conflict between Pewter & Benito. I would put two ramps in if you have the space - reduces potential areas of conflict
It sounds like a lovely space you have for your piggies! I‘d love to see a picture (I love seeing other people‘s set up - I‘m weird like that
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We used spare carpet as a base for our ramp, that seems to work really well and they have a lot of fun pulling strands out
Our ramp is made of wood, correx, and carpet at the bottom, wood on the sides and the top is half a drain. And then we wrapped some fleece fabric around it to make it look nicer. It‘s a real OH original - he fashioned it when I said we need a ramp for the pigs. But they‘ve used it without problems from the start and really like it (Cornelius even sleeps in it from time to time). Good luck with your extension, you‘be got some very lucky boys with all this space!