Building my first official O scale layout

Well, for starters, I'm not sure where you found a piece of plywood that was sold at 5' by 6'.  More than likely, someone found a "ping-pong" table size (5' by 9') and lopped 3' off the long side.  For an "addition," the easiest thing to do is find another ping-pong table size of plywood (if you can) and have the vendor cut it down to a size that will fit your available space.  Since you will have to pay for the whole sheet, be sure to take the "leftovers" home with you.  Some use can always be found for them.

With respect to curves, the answer depends on what type of track you plan to use, sectional or flexible.  Either way, the maximum curve diameter is going to be governed by your narrowest side, 5' in your example.  With sectional track, you will be limited to O54 curve pieces which should allow you a little edge clearance on both sides of the 5' width, but with flexible track, you might be able to squeeze in a 56" diameter with almost no edge clearance on either side.  Since the extra 2" in diameter makes little difference in the equipment you can run, I would suggest staying with O54 diameter curves.  That little edge clearance just might prevent an awful tumble of equipment to the floor!!

Oh, and just as an aside; if you are building a 3-rail layout (and I think you are from the photos), they are more commonly referred to as "O gauge" layouts.  "O scale" more commonly refers to 2-rail layouts.

Chuck

I  have no idea where we got this plywood from. It’s been so long, I had this layout since I was a kid and we just measured it last week. The track I am going to stick with as of right now is just to buy more fastrack, I honestly thought I was limited to 0-42. (In reality 0-48 since 0-42 fastrack doesn’t exist I think). If I can find where I got the plywood from I’ll definitely let you know.

You could also dream bigger and put a wonderful U-shaped layout against the walls in that space, using much of the space between the current layout and the laundry area. What are the overall dimensions of the space from the opening to the stair to the wall behind your soldering area, and between the two stud walls? And what besides a layout MUST go in that space?

I haven’t checked that yet, but the soldering area will be moved over towards the washing machine. Not directly next to it but theirs a little space i can put my soldering stuff.  I can  eventually once we have more equipment to build the layout. I’ll give you the dimensions soon. A U shaped layout sounds nice but we still need room to get around our basement so unfortunately that’s not an option.  

I'd do some thinking on the maximum space both volume and shape you can use, then figure out what will fit.  Don't limit your self to the size of a piece of wood you happen to have.

How would you measure dimensions, this is something I haven’t heard of. Sorry if I hadn’t responded in a while I was busy.