i am in the process of gathering info on a 2-4 piece, med action, 8-9' spinning rod that i will be building for my bro in law. he does a lot of steelhead and salmon fishing along with the occasional walleye and bass. he only wants one rod. i didnt want to spend a fortune building this rod(under $100 total) but at the same time, i want it to last through at least a couple of seasons.
i looked at getting spinning blanks but the ones that come in that length tend to be on the heavier side(he wants something lighter). i looked at fly blanks. i know that this is a possibility. would a 5/6wt match the action of a med-med/hvy action spinning rod? and is there anything else that i need to know before taking on this build? i have never built a spinning rod from a fly blank.

We are talking about a broad range of fishing styles and techniques here. If most of his fishing is for steelhead and salmon I would lean towards a blank designed for that purpose. As for the fly blank, the blank has no idea what you are using it for so if you find a fly blank that you think will work then build it.

I would suggest at least a 6 weight fly to convert to a med. spinning. I have made spinning rods from fly blanks, for different reasons, a few times, with good results. I trimmed the butt or tip to get the action I wanted. I really like to start with a spray rod blank. However, having said that let me add; unless you are experimenting you are better off using a spinning blank in the first place. It's easier to predict the end result.
But if you have a sense of adventure, go for it. You can often find fly or spray on sale so if you don't like the results it's no big deal.
John

Few fly anglers would take much less than an 8 wt. fly rod after steelhead and pacific salmon. You might land some steelhead and salmon with a spin rod built on a lighter fly-rod blank, but you risk fighting them to death.
On the positive side, you can find lots of 4-piece fly rod blanks from many price ranges to build into a spin rod. If an angler has to fly to his fishing destination the 4 piece blank is a logistical blessing.

Cheng, see Utmost's site listed at the left. Check out their closeout blanks for the steelhead blanks. They are 2 piece and have two different weight ratings in an 8 1/2 rod. It could be what your looking for.

I just built a spinning rod with a 9ft 4pc 10wt blank to take to Baja. I couldn't find a multi piece spinning blank for travel so I opted for the Tiger Eye saltwater fly blank. It's a great value. It'll throw up to 3/4 ounce lures and has a nice med fast action.

A few months back I built a "salmon/steelhead" spinning rod from an 8 weight blank that I had spare. It is nice for casting light rigs but is definitely as light as I would go. I'm planning a silver salmon trip to AK later this year and wish it were built from a 10 weight.