Barry wrote:

<<Now, i'd like to do it nominative/accusative style, but
i'm not sure how it works with both transitive and intransitive sentences.
Also, how are subordinate clauses, and complex sentences handled?

And, for the cases that mark roles other than nominative/accusative, how
do they work within the sentence?>>

This is kind of a hard question (which may be why there've been no
responses).   It's kind of like asking, "What's a linguist do?"

Using your paradigm, let's say that /lanal/ is "cry" in the present and
/gampal/ is "hit" in the present, and /peler/ is "stick".   Here are some sentences
(with SOV word order):

manath lanal.   "The leaf cries."
peler lanal.   "The stick cries."
manath pelermas gampal.   "The leaf hits the stick."
peler manathmas gampal.   "The stick hits the leaf."

That's how it works with transitive and intransitive verbs.   (To be more
correct, that should be "That's how it *could* work", or maybe "That's how it
*usually* works", or still "That's it how it works in IE languages like Latin".)

I'm not sure what you mean by a complex sentence, so I'll skip that.   For a
subordinate you mean like "I want to eat"?   Or how about "The
leaf wants to hit the stick", where /vamal/ is "to want" in the present, and
/gampas/ is the infinitive of "hit":

manath pelermas gampas vamal.   "The leaf wants to hit the stick."

However, this brings us to another point.   Sometimes languages will assign a
case other than the nominative to subjects of experiencer verbs.   So even if
the nominative is your "subject" case, you might put the subject of "to want"
in the Dative.   In which case the above would be:

manathiul pelermas gampas vamal.

As for "how do all the other cases work", well, they work like prepositional
phrases in English, kind of.   So if you said:

manath pelerod lanal.

You'd be saying that the leaf cried with the aid of a stick.   In theory, you
should be able to stick as many in there as you wanted.   So you could also
say, given that /torog/ is "house":

manath pelerod torogsei lanal.   "The leaf cries with a stick at the house."

Also, the dative is often used like a benefactive, in which case you could
get, given that /saskan/ is "boy":

manath pelerod torogsei saskaniul lanal.   "The leaf cries with a stick at
the house for a boy."

(Your language will probably have rules about what order these things can go

With a couple of your cases, though, it wouldn't make sense.   After all,
with the allative ("to x") or the ablative ("from x") it wouldn't work, 'cause
you usually don't think of crying as something that happens to or a from a
place.   With those two, you could only use them with motion verbs.

Lastly is the genitive.   In Latin, the genitive was sometimes used for
certain types of subjects (based on the verb) and certain types of objects.   But
generally, you saw it like this:

manath pelersar.   "The leaf of the stick."

And if you were going to have it acting like this, you couldn't separate
those two nouns, or else it wouldn't work.

And that's how a typical Latinate conlang using the cases you came up with
might work.   However, cases can do much more interesting things.