Kono hon ha omoshirokute mijikakatta desu.
Two things to watch out for. First, Japanese adjectives can be put into the past tense, so you don't need "Deshita" at the end, you put the adjective in the past, and leave the copula "Desu" in the present.
Secondly, when you put a lot of adjectives together, you usually put them together like this:
Kono hon ha omoshirokute benride ookikute kireide takakatta desu.
In other words, except for the very last adjective, the 'i' adjectives lose the 'i' and take 'kute' (or sometimes just 'ku') and the 'na' adjectives lose the 'na' and take 'de' instead.
I'm not explaining this well, but any basic Japanese grammar book will explain this in detail near the first few chapters. Good luck fella.
Sorry! Edited for massive kanji-hiragana failure. For some reason EG won't display mine properly. >.<
Edited by Telepathic.Geometry at 01:16:46 27-09-2012