After Starting with the Cygnar Battlebox and purchasing the items from The Cygnar Toolbox, you might find yourself wanting to expand your army using Major Markus 'Siege' Brisbane, a ranged warcaster specializing in cracking armor.
What to Order
Seige does not work exceptionally well with the battlebox. He doesn't really need an arcnode. And the Ironclad and Charger are both too focus hungry for him. If you are looking to expand the battlebox then Seige is not the way to go as you will be basically buying a whole new army for him. However, he does work well with alot of units that are popular with other casters. Units like Gunmages, B13, Defender and Squire go well with most Cygnar casters.
Once More Unto the Breach
Major Markus 'Siege' Brisbane

Siege Brisbane creates opportunities to fire at the enemy with the Foxhole Spell, and tears up the heavies using his Breach Feat to halve the enemy's base ARM. It's a tricky feat to use, however, as the hit makes the feat expire on that model.
Seige is a "toolbox" caster. His primary method of victory is assasination, but his feat and spells allow him to deal with a wide range of targets.
Breach can be used for assasination or to destroy the enemy. Most breached warcasters can easily be one-shotted by Seige or a Defender under the feat if they are not camping all their focus or have other defensive measures in place. Even then it will usually leave a big dent that a second shot can finish them off even withhout Breach. On assasination runs against warlocks be aware that if the warlocks transfers dmg it removes the breach effect from both the warcaster and the beast. So either shoot the beast first or just realise that one shot is going to get transferred. If you want to decimate the enemy it is particularly effective against units and solos. Even heavy, 8 wound infantry, can go down to single pow 10s from gun mages. Try to catch as many bad guys in the feat as possible, but make sure you have the attacks needed to deal with them. If used well, you can wipe out the majority of the enemy force in one round. Especially infantry heavy forces.
Mage sight and Ground Pounder both allow him to ignore stealth. Ground pounder is a very nice "aoe" as well to deal with large infantry units. It is placed so you can cover as many models as possible. Also it does full damage to all models. You do have to roll a seperate "to hit" roll for each model, though. If you need to boost to hit then it can get expensive fast.
Mage sight also allows Seige and his Battlegroup to ignore forests. This is great for targetting a caster or model that your opponent thought was safely hiding in or behind the woods. As another placed template you do not need to target or roll to hit the enemy.
Foxhole can be used offensively of defensively. Defensively it gives you cover and immunity to blasts. Offensively it allows you to drop screening models out of the way to get to the models behind them. This doesn't count as an offensive spell so you place the template and it automatically works. No need for any "to hit" rolls. This is particularly nice for assasination runs where the warcaster is hiding behind his troops.
Explosivo makes a normal shot and aoe shot and makes it a magical shot to boot. Good for dealing with a variety of targets including stealth solos, incorporeal models and choir protected menoth jacks.
Force Hammer and Rift are situational. Both are expensive and take away from the focus he can use for shooting. They are not cast often, but remember them when you need them. Moving badguys and creating rough terrain can both be very useful.
Most Seige lists have 3 auto-includes: Defender, Squire and Reinholdt.
The Squire extends Seige's control range. This is important because the range of his feat and his two most important spells are all CTRL. A bigger control area means his threat is increased and his feat is more effective. The ability to reroll a magical attack is nice for the rare times you cast Force Hammer or Rift. However, when you do use them you probably want to make sure you hit. The extra focus also helps as it gives him a bit more to play with. An extra boost or ability to cast that one extra spell may be the difference.
Defender is pretty obvious. It gives Seige another big gun. It also can be used to block LOS to Seige and the hammer makes it a decent melee combatant for the inevitable counter charge. Remember not to use the hammer on warjacks for the Feat turn, though. The cortex damage cancels the feat before the hit from the hammer gets thru. A second defnder is often taken for Seige lists and Jack Marshalled to Gunmages or a Jr. Warcaster. Seige himself does not like too many warjacks as he keeps his focus for himself.
Reinholdt is also pretty obvious why you should take him. He allows Seige to shoot his Rocket Launcher twice instead of once, doubling his firepower. One common error is thinking that Reinholdt allows Seige to use his Ground Pounder attack twice. It does not becasue Ground Pounder is a * attack. It only allows a second regular rocket attack.
A Strong Offender is a
Defender

- PIP 31062 (Heavy Warjack kit. Build with a right arm hammer and left arm giant gun.)
The Defender has range, high POW, and hits like a killer with the Breach Feat. Cast the Explosivo Spell on it and you have a POW 15 AOE.
Infantry Screens
Sword Knights

- PIP 31029 (Minimum unit box)
- PIP 31030 (Buy two blisters for a maximum unit)
There isn't really a special interaction here. Sword Knights are simply an inexpensive infantry melee screen that has some staying power due to the Defensive Line Ability.
Precursor Knights with UA are also worth considering. They do not need much support and with their mini-feat can do alot of damage, especially on Seige's feat turn. Their ranked attacks ability also allow Seige and others to ignore them when shooting. They also have better defensive abilities. They do cost more, points-wise, than Swordknights, but also bring alot more to the table.
Black 13 is a great unit for any caster. They are able to deal with alot of various threats with little to no support.
Gunmages are another great choice. They are great for dealing with all but the heaviest armor. But that is why you have Seige and his feat. they can easily deal with stealth units and solos. However, their best ability is being able to jack marshal a warjack and give them access to all their special shots. If you want to take a second defender this is a great place to put it. The ability to gain Snipe or Critical Brutal is excellent. Use your marshall boost on the to hit roll and increase your odds of a critical.
Fire in the Hole
Trencher Master Gunner
The Trencher Master Gunner can extend the range of your Defender if you cast Explosivo on the 'jack first.
Other solos to consider are the Squire (mentioned above), Jr. Warcaster and Arlan Strangeways.
Jr. Warcaster can control that second defender and cast arcane shield on a unit. They bring a nice buff to your army that Seige does not.
Arlan works well with jackmarshalled warjacks since he can provide them focus. His other abilites are good as well and he provides alot of support.
Need More Firepower?
Reinholdt, Gobber Speculator

Get more shots for Siege's Rocket Launcher with the reload ability.
Sample 35 Point Army List
Starting with the Cygnar Battlebox and The Cygnar Toolbox and adding the models above, you can make some of the following list:
Points: 35/35
- Major Markus 'Siege' Brisbane (*5pts)
- Charger (4pts)
- Defender (9pts)
- Squire (2pts)
- Black 13th Gun Mage Strike Team (4pts)
- Sword Knights (Leader and 9 Grunts) (6pts)
- Journeyman Warcaster (3pts)
- Reinholdt, Gobber Speculator (1pts)
- Trencher Master Gunner (2pts)
Conclusion