わたしのへや

わたしのへやはくらいとひろいとしろい。

"dark and" and "large and" should be くらくて and ひろくて respectively here. So くらくてひろくてしろい(dark, large, and white) is correct grammatically. However, it would sound a little bit awkward. For example, you can write like くらいけど、ひろくてしろい(dark but large and white) instead.

わたしのへやにつくえとえとほんだながあります。

This is completely correct. It would be more fluent to say わたしのへやには than わたしのへやに in order to describe what things are in your room.

Anyway, your writing was really good and fully understandable.

Keep up the good work!