Hello.
My dome is made up using 2.4 x1.2 metre sheetsof 4mm marine ply. Simple reason to end up with a 1500 diameter dome.
If you go for a 3m dome. You're going to have to join the sheets longitudinally. Which is darn difficult when you want to put such a bend in. Unless you go for an apex oriented vertical segment design.
Mine was designed to be easily constructed by a wrinkly old chick on her own.
I made up the base rings with a rather inferior ply . I should have used 18mm good stuff.
And the flat roof section should also have been 18mm. False economy to go less.
The design was drafted by me in AutoCAD. Not hard to do but you need to be a little agile mentally unless you use it all the time.
I dont think a vertical segment system is a bad idea. I just felt it was more difficult to manoeuvre in construction.
If you look for Southern astronomical society magazine "Event Horizon"Jan edition on
www.sas.org.au I did a blog and some pics. There's also some on the diy obsy forum on this site I think.
Cutting out the segments accurately is critical if you want it to conform to the plamned shape.