How to build around metal column

I'm not sure how long these walls are going to be, but here is a common method using wood studs, even though I still think steel framing would be better in your situation. First step is to secure 2X4's or 2X6's along a chalk line on the floor at wall placement position. This will be the first or two bottom plates. Transcribe location of obsticles onto this bottom plate using a laser or plumb bob. Lay out and scribe the corners, studs, jacks etc onto this plate. At this point you will know where conflicts with the pipes, vents and will be able to plan prebuilt wall sections around them. or areas where a horizontal needs to be added below the obsticle height to allow wall to be fitted. Now lay out your top and bottom plates against the now scribed secured bottom plate and transfer the layout marks to them. (Yes, there will be two bottom plates when you are done.)

Side note: using the fixed bottom plate allows easier and tighter fitting prefab walls to be lifted into place without the angle problem of lifting the wall and having to make the wall 3/4" short to compensate for the lift angle.

Now you can lay out the plates, studs etc and assemble the wall sections with a nail gun,or hammer (uggg) nailing studs through the bottom and top of the plates, so no toe nailing required. Because of your height, a rolling staging or scissor lift would be a great help. Lift the sections to vertical and slide them onto the pre-secured bottom plate. Flush them to this plate and nail the bottom. Now plumb the wall and nail to the ceiling, being sure to check plumb every few feet. This method will allow you to make several smaller wall sections and build around the pipes. Install horizontal nailers just below the pipes/vents etc.

Jay's plan to use beam pockets in the front wall will work fine. Dbl. top plates with no additional structure supporting a roof over a SIX foot span (as per Tester101's first suggestion) is entirely inadequate. Whether a 2x beam on edge is adequate, and how deep it is, depends on what the roof snowload is, if any.

There are also hardware beam hangers available that support the end of the beam and are nailed or bolted to the supporting studs in the front wall, eliminating the need to frame pockets. Tester101's second suggestion to use a ledger to support the beam end is a viable idea, but the connection of the ledger under the beam, into the studs needs to be carefully detailed.

A metal plate tying the two walls together is an important detail. Alternately, extend the dbl. top plates over the beam, lowering the beam 3" so the plates can still lap in a conventional manner. If you go with a hardware hanger or a ledger, the beam should be strapped to the sidewall top plate to hold it to the main structure in a wind storm or possibly an earthquake.

Along wind storm lines, be sure the beam is well connected to the outer post, and the post tied into the foundation, as there can be significant uplift forces on an open porch roof.