Simple, free blueprint making program? Or, learn me building a carport

So, long story short is i berkeleyed up, and its snowballing into epic proportions. 

I have to move an existing metal carport and lawnmower shed due to setback and property lines. 

Im planning to grade the area properly, and then pour a slab. Erect a simple structure on top. 

I would like to combine both buildings into one, as well as make them weathertight and lockable. 

I would like to store 2 cars, my tow dolly, my riding mower, my lawncare crap, etc in it. 

Existing carport is 18 wide, 21 deep. Shed is 8 wide, 12 deep. My tow dolly is on the neighbors land under a tarp (she hasn't noticed in over a year, nor has she said anything about the carport on her land. But its time to fix it now that i know about it)

I have ideas in my head i can't describe to my wife, my friends, or the city. I also dont know how big ill need to make it, or how things will need to lay out. 

My plan is enclosed pole barn style. 6 inch concrete slab, french barn doors, tin roof. No power/water/insulation or anything. 

Ive never tried to design from scratch. Ive built from free plans, or with the help of family. So I'm in uncharted territory for me here. 

What programs/apps can u download to start? What questions am i not asking of you or myself? Where do i begin?

I don't know about free home design programs, but SketchUp is free and easy to learn. Plus there is the SketchUp Warehouse, where people upload premade objects you can use for free.

Its not ideal but the learning curve is low and you can paint with materials like grass and wood and concrete so it gets the point across wuickly and easily.

I can talk you through the basics quickly.

You can get a 30-day trial of RevIt from the Autodesk website for free, if you can work fast.

I have a tutorial on building a garage just to learn the software, which may be of help:

https://www.gwellwood.com/subjects/drafting/revit-tutorial-two-car-garage/

In reply to SkinnyG (Forum Supporter) :

Revit is awesome, but the learning curve is steep and the hardware requirements are hefty.

I use Revit every day, so I'll be glad to advise on that too.

Thanks y'all!!

I was able to find a picture of what im GENERALLY thinking. Wife has to sign off on exterior details like siding/tin/painted plywood/etc.

I also need to do a lot more research on this style of building, as I'm realizing what i think i know isn't nearly enough to even know what i dont know. 

Fist blush is 6x6 on 10ft centers, attached to the slab via brackets and tapcons. Then, 2x4 studs in between on 2ft centers for exterior cladding. 2x6 or 2x8 on roof beams perpendicular to long axis on 2ft centers, cross bracing between on 4ft centers. 1/2 osb roof sheeting, covered by tarpaper, covered by tin. 

9ft wide, 8ft tall french barn doors on each bay.

I think. 

In reply to Duke :

My daughter studying architecture and says after 2 years Revit is challenging big time.

A 6 inch slab is only really needed if you are gonna drive very heavy stuff on it, 99 percent of garages/car ports/driveways are 4 inches and it's more than adequate for normal cars