Attach vertical supports to visible sides of deck. Screw offcut timber blocks to back of deck frame going down towards ground. Screw blocks to these flush with face of deck frame. Place supports near corners and 600mm apart.
Screw decking board across joist 465mm from end. Cut and loose-lay decking back towards end of deck, joining over joists where required. Overhang decking at side of deck. Temporarily fix face board to frame at end of deck so top edge is flush with decking boards.
Screw first decking board to joist with a 3mm plastic packer to face board to create gap. Use chalk line to create a screw guide between screws on this board and board fixed in Step 3. Place 3mm packers between boards and screw to joists. Repeat for all joists along deck.
Repeat Steps 3 and 4, measuring from last board fixed, to complete deck. Cut off overhanging decking at side flush with joist.
Place sleeper on edge on ground in line with frame at end of deck. From this, run sleepers along side of deck and fence. Make level, excavating if required. Screw through sleeper at end into those at sides. Continue laying sleepers along sides. Screw an offcut over joins in side sleepers. Finish with a sleeper in line with frame at other end of deck.
Construct stud frame to desired seat length, here 2230mm. Make overall height of frame the distance from top of sleepers laid in Step 6 to seat height above deck, here 372mm, less decking thickness. Nail frame together with stud spacing not exceeding 450mm. Repeat for second frame.
Place stud frame in position on side sleeper and nail. Repeat for second stud frame on other side of seat. At each end of stud frame, place a sleeper between side sleepers flush with their top for planter box base.
Cut and lay sleepers to build up planter boxes, screwing together as you go. Cut final sleeper along its length so top of planter box is 186mm above seat frame.
Using offcuts of sleeper, create 50mm square battens and screw to inside corners of planter boxes. Make top of batten finish 60mm from top of planter box. Cut sleeper (or any spare offcuts) into 60mm-wide strips. Run strips around inside top of planter box to support capping.
Cut cross pieces to suit overall width of seat. Notch corners so top edge will be flush with top of stud frame. Nail into studs to hold, then screw with 85mm galvanised batten screws.
Fix decking along face of planter box and seat. Overhang ends of planter box by 19mm (thickness of decking). Leave a 3mm gap to deck and between boards. Make sure edge of boards at seat and top of planter box are proud by 19mm so they end up flush with seat decking and planter box capping.
Fix face board to side of deck frame so edge is flush with decking. Run boards across ends of planter boxes to complete built-in look. Fix boards down vertical supports (see Step 2) and up ends of planter boxes, keeping a 3mm gap between boards.
Cut and fix decking to seat as with main deck (see Step 8). Cut and fix decking to sides of planter box above seat.
Cut and fit decking for capping to top of planter boxes. Mitre joins in corners.
Allow timber to weather for four to six weeks to allow tannins to leach out. Clean timber using deck cleaner, then apply two coats of decking oil, allowing to dry after each coat.
Use metal screws to fix aluminium screen to fence.