"This is a big cupboard."
Translation:Seo preas mòr.
I'm far from being an expert but I believe, when used in this way you don't need a separate verb because 'seo' here means 'this is'. It's like when introducing somebody "Seo Màiri" = "This is Mairi". If however, you wanted to say "this big cupboard" it would be "an preas mòr seo"