I don't know the exact Arabic, but here is the principle (I believe): When you say "This is a spacious kitchen", the words are This Kitchen Spacious.
When you say "This kitchen is spacious" the words are TheKitchen TheThis Spacious.
When you say "This spacious kitchen" the words are Kitchen Spacious Thethis. In other words, you need to add the in various places and move the words around. Hopefully someone will give us the actual Arabic.
The difference is the use of the definite article ال. If you do not use the article in front of the noun (kitchen, in this case), you are saying "this is a kitchen." If you use the definite article (making it a specific kitchen), you are saying "this kitchen is ... " followed by whatever you are describing it as.