This is a Lego model of the Stargate Universe starship Destiny. Originally it was going to be a large cargo ship or carrier, but once I made some progress I decided to modify it to resemble the Stargate craft. Because of the complexity, a step-by-step guide would be next to impossible, but this outline should be able to give you an idea of how to build it.
Step 1: Superstructure
The main structure of the ship is composed mainly of vehicle chassis, large bricks, and structures reused from previous starships. To combine them, I used technic parts to combine the chassis and a sort of tight "clamp" with bricks. The walls are basically made of bricks just like any Lego house, but on the sides the wings are built into the wall in several locations to add stability. As you can see, the wingspan is just short of the length of the craft, so support is key to preventing their collapse.
Step 2: Engines
The ship has 17 thrusters, all but 3 of which are simply wheels attached to the wing structure. The larger ones are built like turbines into the body of the craft. The engines are built into the support structure for the wings, mostly vehicle chassis again, which helps hold the wing support into the superstructure (as you can see, support is key to this whole build).
Step 3: Bridge
The bridge is the least stable part of the ship, since as I was building the superstructure I wasn't planning on building Destiny. In this model the bridge is built on top of a tower from an old construction set (the large blue piece in the previous pictures). It is then constructed from the main structure of the Mars Mission Alien Mothership. Inside is a little cramped, but there is enough room for several control panels for an operator crew.
Step 4: Bowsprit
The bow is mostly composed of stacked plates since they are easy to extend the long distance. Also present is another cab for a forward operator and several shield generator prongs (creative license). The main pilot operates via a Matrix-like thought interface control compartment at the back of the bowsprit (under the green semicircle on other pictures).
Step 5: Weapon Systems
This is usually a purely aesthetic part of construction, but in this case I added a large particle wave cannon located directly under the bridge. Between the spring-loaded nuclear missile launchers is a black pyramid-shaped structure hiding the cannon. To build it I used technic bars to make a sort of parallel arm that folds forward out from under the bridge.
Aside from that, you can add whatever weapons you like. Also on this craft are a pair of torpedo tubes (located on each side of the bridge directly in front of the larger rear thrusters). The rotary barrel guns (this picture; used a turntable and hinge) were added for the resemblance factor.
Step 6: Size Comparison
I'm not sure about the Stargate Destiny, or the Venator-class Star Destroyer, but in the case of this Lego model the Venator is only about half as long as Destiny. For simplicity, you could easily build it smaller.