We bought a house with a small barn about 30x40 with a few horse stalls in. Currently using some of the stall to hold some of my equipment/junk. I keep thinking about making more storage room since we want to get some animals. I have some room on the back of the barn I could build a lean to. Just cover the top and sides for now. Maybe 10 deepx20 long at the absolute biggest. I'm assuming I would need to set my support posts in concrete. I have never built a structure like this so just asking for advise. I live in northern Ohio.

 

Setting posts in concrete is not always the best option, because if and when they ever rot off you are kind of stuck. It's usually better to pour a cement pier (sonotube) and then set your posts above grade on a post bracket. (Simpson PB66) Posts should be pressure treated and specifically say that they are rated for ground contact.

With 20 feet to span you would likely want 3 posts... 6x6's that are 10' on center. The 6x6's would need to be notched on one side to accept a 20' long lvl beam, which would be bolted through the 6x6 with pairs of 1/2" x 7 hdg bolts. Your rafters would likely need to be minimum 2x8's, placed in joist hangers, (Simpson LUS28) fastened to the ledger (a 2x8 fastened with ledgerloks to each stud on the existing side of the barn) and to the lvl in front.

If you plan to use metal sheeting for the roof, you would put 2x4 purlins perpendicular to your rafters every 24-32" or so, to have something solid to walk on and screw to.

You will want the pitch of the roof to be at least 2:12 which means that if the projection of the roof is 10 feet, the rise from your beam in front to your ledger in back will be 1/6th of 120"... (20" rise.)

 

What would be a cost estimate to build something like this.

 

Impossible to know what it will cost.
You need to make up a materials list and take it someplace local to find out.
And no a ball park figure will not do you any good.

 

If you are going to DIY it's probably around $1000 in materials.

 

Depending on the quality of the barn wall that will have the ledger board attached, you may also want to add 3 vertical supports (resting on cement piers) for the ledger board across the 20 feet. The outer supports will become part of the framing for the side wall of the lean-to. The majority of the lean-to roof vertical weight at the barn wall will be carried by the 3 added vertical supports, not the barn wall.

 

I'm thinking about just buying a small storage shed. Rural King has an 8x10 for under 400. Just debating bif I even have time to build one. Just the roofing would probably cost more than that