hi,
first off, im a big fan of scratch builds, and models that generally havent been done before, as not only is it a challege, but the end results are well work it, if you check out my Optimus and ravage ive just done, these were built from the toys, i simply scaled up, then changed things here and there, on prime, i changed things to stop it looking like a giant toy, on ravage i gave him extra joints in his tail,legs,neck and head, but both my models were based on toys, you could get a mouser toy, and scale it up, then look at pics of mousers and go with the one that looks the best, it depends on the look your going for too, if you go for the cartoon look, it will look less mean, but the eastman and laird look will probaly look gritty and mean, its finding a happy meduim on what you want, i build in wood and styrene, and use car filler to lose joints, add curves etc, hope this helps, and if you need any help drop me a line mate
all the best
colin