There are a load of photos of housing in the 'Stories & Photos' section. Might be worth checking these out for ideas.
We are in process of converting half of the shed for our two buns (other half will be for storage of their food, etc) and they will have access to a run which is 12'Lx6'Wx4'H. Once shed has been done we will be putting hatch thru to the run which we will close at night.
I managed to pick up a 12x10 shed on ebay for £15 which was a complete bargain. My husband is having this one for his motorbike and tools, etc and I am having his existing shed which is 10x8. There are always sheds and hutches, etc advertised on freeads, gumtree and preloved so worth checking these out for your local area.
The run isnt quite finished yet but this is where its at so far:
My husband put this together. Most of the wood was salvaged from an old farm gate that had been dumped and he managed to get the tubes for the tunnel from a mate of his who does construction work with roads, etc. The only thing we have had to buy to do this was the mesh. I had a bargain with this on Ebay again lol. I got a 30 metre roll for £36.00 and this included postage. Can dig out the link for this if you like - just PM me if you're interested.
As you can see, we've been lucky to have done all of this quite cheaply so far so its worth having a scout around for various materials. Not sure if this is any help to you but hopefull so.
Good luck with whatever you decide to do!