So... I can't build your list for you. I can't even build a list that wins every match for me and makes people afraid for myself, so I'm not going to promise you anything either. Also, unless things have very much changed around ATT since I last read the primers this style of thread isn't well received because it doesn't actually add anything to the forum. It doesn't get people thinking about their own lists, nor does it provide interesting new points of view; it just asks someone to construct something using a certain pool or resources (don't get me wrong... building stuff from finite resources is one of my favourite games... it's just not the typical thing ATT endorses). With that said, here are some pointers I have gleaned from competitive play and talking with other competitive Tau players.
The Support'O - If someone fields a Shas'O without weapons on him, seasoned players know they are in for a harder battle. It means he is packing a C&C node and a MSS and he's going to grant whatever unit he is with rerolls to hit and negates cover.
Riptides - I rarely see competitive lists without riptides. I say riptides not riptide because 40k demands redundancy. One will likely be shot to pieces and die (a good distraction for a turn or two if that's what you're looking for)... but two will make things nasty for your opponent. I know from personal experience that a pair of riptides is just gross.
Farsight Supplement allies - what is better than battlesuits? Battlesuits as troops (note: all battlesuit armies are not super competitive, a mix of troop types works much better). The more rules you have the more rules you can abuse, so adding in a whole other mini-codex is worth considering (especially when that mini codex has an independent character riptide... who could... say... join another riptide... and then maybe... I don't know... be joined by the Support'O to create a unit that fires a pair of of rerollable ignores cover S8 large blast templates? Nooo... that would be crazy. Note: it works, but consensus among most of the tournament Tau players was that the unit was just a tad lackluster and that more troops would have served the army better than an IC riptide).
Combos combos combos - Tau is all about creating a synthesis of overlapping firepower. The units I am listing above are typically ones you see in competitive lists, but they can only work if the rest of the army fills the gaps and everything fills its roles to bring together something that is much greater than the sum of its parts. Whatever you go with ask yourself "if I pick this what do I need to make sure the army as a whole can take on any threat?" It's tempting to spam a single good unit (like the early days of Tau and the 3+ riptides), but those lists didn't stay in the competitive scene for long for a reason; they lacked the stuff that holds Tau all together. Almost everything in our book can work and can be scary... but given how well balanced it is... making it work is up to you.